Add line numbers option to rustdoc

Fixes #22878.

r? @QuietMisdreavus

Cleanup rustdoc tests with `@!has` and `@!matches`

Fixes #49713

Here's a _long_ list of all the places that include `@!has`. I have marked the ones I have looked at so far.

 - [x] search-index.rs:        fn priv_method() {} // @!has - priv_method
 - [x] search-index.rs:        fn trait_method(&self) {} // @!has - priv_method
 - [x] search-index.rs:    // @!has search-index.js Target
 - [x] short-dockblock.rs:// @!has foo/index.html '//*[@class="docblock-short"]/p/h1' 'fooo'
 - [x] short-dockblock.rs:// @!has foo/index.html '//*[@class="docblock-short"]/p/h2' 'mooood'
 - [x] keyword.rs:// @!has foo/index.html '//a/@href' 'foo/index.html'
 - [x] keyword.rs:// @!has foo/foo/index.html
 - [x] keyword.rs:// @!has-dir foo/foo
 - [x] issue-46380-2.rs:// @!has - '//*[@class="impl"]' 'impl PublicTrait<PrivateStruct> for PublicStruct'
 - [x] escape-rust-expr.rs:// @!has escape_rust_expr/constant.CONST_S.html '//pre[@class="rust const"]' '"<script>"'
 - [x] issue-33069.rs:// @!has - '//code' 'impl Bar for Foo'
 - [x] playground-empty.rs:// @!has foo/index.html '//a[@class="test-arrow"]' "Run"
 - [x] issue-34473.rs:// @!has - SomeTypeWithLongName
 - [x] issue-34473.rs:// @!has - SomeTypeWithLongName
 - [x] issue-34473.rs:// @!has foo/struct.SomeTypeWithLongName.html
 - [x] issue-29584.rs:// @!has - 'impl Bar for'
 - [x] hidden-line.rs:// @!has hidden_line/fn.foo.html invisible
 - [x] manual_impl.rs:// @!has - '//*[@class="docblock"]' 'Docs associated with the trait a_method definition.'
 - [x] manual_impl.rs:// @!has - '//*[@class="docblock"]' 'There is another line'
 - [x] manual_impl.rs:// @!has - '//*[@class="docblock"]' 'Docs associated with the trait a_method definition.'
 - [x] manual_impl.rs:// @!has - '//*[@class="docblock"]' 'Docs associated with the trait c_method definition.'
 - [x] issue-19190-2.rs:// @!has - '//*[@id="method.new"]' 'fn new() -> String'
 - [x] unneeded-trait-implementations-title.rs:// @!has foo/struct.Bar.html '//*[@id="implementations"]'
 - [x] masked.rs:// @!has 'search-index.js' 'masked_method'
 - [x] masked.rs:// @!has 'foo/struct.String.html' 'MaskedTrait'
 - [x] masked.rs:// @!has 'foo/struct.String.html' 'masked_method'
 - [x] masked.rs:// @!has 'foo/trait.Clone.html' 'MaskedStruct'
 - [x] masked.rs:// @!has 'foo/struct.MyStruct.html' 'MaskedTrait'
 - [x] masked.rs:// @!has 'foo/struct.MyStruct.html' 'masked_method'
 - [x] masked.rs:// @!has 'foo/trait.MyTrait.html' 'MaskedStruct'
 - [x] redirect.rs:// @!has - '//code/a' 'Qux'
 - [x] issue-43701.rs:// @!has implementors/core/clone/trait.Clone.js
 - [x] union.rs:    // @!has - //pre "b: u16"
 - [x] prim-title.rs:// @!has - '//head/title' 'foo'
 - [x] empty-section.rs:// @!has - '//*[@class="synthetic-implementations"]' 'Auto Trait Implementations'
 - [x] traits-in-bodies-private.rs:// @!has - '//code' 'impl HiddenTrait for SomeStruct'
 - [x] playground-none.rs:// @!has foo/index.html '//a[@class="test-arrow"]' "Run"
 - [x] issue-34025.rs:// @!has 'foo/sys/index.html'
 - [x] issue-34025.rs:// @!has 'foo/sys/sidebar-items.js'
 - [x] issue-34025.rs:        // @!has 'foo/sys/fn.foo.html'
 - [x] issue-23812.rs:// @!has - '/// Outer comment'
 - [x] issue-23812.rs:// @!has - '//! Inner comment'
 - [x] issue-23812.rs:// @!has - '/** Outer block comment */'
 - [x] issue-23812.rs:// @!has - '/*! Inner block comment */'
 - [x] pub-use-extern-macros.rs:// @!has pub_use_extern_macros/index.html '//code' 'pub use macros::bar;'
 - [x] pub-use-extern-macros.rs:// @!has pub_use_extern_macros/index.html '//code' 'pub use macros::baz;'
 - [x] pub-use-extern-macros.rs:// @!has pub_use_extern_macros/macro.quux.html
 - [x] pub-use-extern-macros.rs:// @!has pub_use_extern_macros/index.html '//code' 'pub use macros::quux;'
 - [x] issue-26606.rs:// @!has - '//a/@href' '../src/'
 - [x] foreigntype-reexport.rs:// @!has foreigntype_reexport/foreigntype.X4.html
 - [x] foreigntype-reexport.rs:// @!has foreigntype_reexport/index.html '//a[@class="foreigntype"]' 'X4'
 - [x] issue-31899.rs:// @!has - 'rust rust-example-rendered'
 - [x] issue-31899.rs:// @!has - 'use ndarray::arr2'
 - [x] issue-31899.rs:// @!has - 'prohibited'
 - [x] hidden-trait-struct-impls.rs:// @!has foo/struct.Bar.html '//*[@id="impl-Foo"]' 'impl Foo for Bar'
 - [x] hidden-trait-struct-impls.rs:// @!has foo/struct.Bar.html '//*[@id="impl-Dark"]' 'impl Dark for Bar'
 - [x] hidden-trait-struct-impls.rs:// @!has foo/trait.Bam.html '//*[@id="implementors-list"]' 'impl Bam for Hidden'
 - [x] hidden-impls.rs:// @!has - 'Foo'
 - [x] hidden-impls.rs:// @!has - 'Foo'
 - [x] module-impls.rs:// @!has foo/index.html 'Implementations'
 - [x] issue-35169.rs:// @!has - '//*[@id="by_mut_ref.v"]' 'fn by_mut_ref(&mut self)'
 - [x] issue-35169.rs:// @!has - '//*[@id="method.by_mut_ref"]' 'fn by_mut_ref(&mut self)'
 - [x] issue-35169.rs:// @!has - '//*[@id="by_explicit_mut_ref.v"]' 'fn by_explicit_mut_ref(self: &mut Foo)'
 - [x] issue-35169.rs:// @!has - '//*[@id="method.by_explicit_mut_ref"]' 'fn by_explicit_mut_ref(self: &mut Foo)'
 - [x] issue-35169.rs:// @!has - '//*[@id="by_explicit_box.v"]' 'fn by_explicit_box(self: Box<Foo>)'
 - [x] issue-35169.rs:// @!has - '//*[@id="method.by_explicit_box"]' 'fn by_explicit_box(self: Box<Foo>)'
 - [x] issue-35169.rs:// @!has - '//*[@id="by_explicit_self_box.v"]' 'fn by_explicit_self_box(self: Box<Self>)'
 - [x] issue-35169.rs:// @!has - '//*[@id="method.by_explicit_self_box"]' 'fn by_explicit_self_box(self: Box<Self>)'
 - [x] issue-35169.rs:// @!has - '//*[@id="static_foo.v"]' 'fn static_foo()'
 - [x] issue-35169.rs:// @!has - '//*[@id="method.static_foo"]' 'fn static_foo()'
 - [x] extern-links.rs:// @!has foo/index.html '//a' 'extern_links'
 - [x] extern-links.rs:// @!has foo/index.html '//a' 'Foo'
 - [x] extern-links.rs:    // @!has foo/hidden/extern_links/index.html
 - [x] extern-links.rs:    // @!has foo/hidden/extern_links/struct.Foo.html
 - [x] issue-33178-1.rs:// @!has - //a/@title empty
 - [x] issue-33178-1.rs:// @!has - //a/@title variant_struct
 - [x] issue-47038.rs:// @!has - '//*[@id="macros"]' 'Macros'
 - [x] issue-47038.rs:// @!has - '//a/@href' 'macro.vec.html'
 - [x] issue-47038.rs:// @!has 'foo/macro.vec.html'
 - [x] issue-46766.rs:// @!has foo/index.html '//a/@href' './Enum/index.html'
 - [x] issue-32395.rs:// @!has - 'pub qux'
 - [x] issue-32395.rs:// @!has - 'pub Bar'
 - [x] issue-32395.rs:// @!has - 'pub qux'
 - [x] issue-32395.rs:// @!has - 'pub Bar'
 - [x] hidden-methods.rs:// @!has - 'Methods'
 - [x] hidden-methods.rs:// @!has - 'impl Foo'
 - [x] hidden-methods.rs:// @!has - 'this_should_be_hidden'
 - [x] hidden-methods.rs:// @!has - 'Methods'
 - [x] hidden-methods.rs:// @!has - 'impl Bar'
 - [x] hidden-methods.rs:// @!has - 'this_should_be_hidden'
 - [x] structfields.rs:    // @!has - //pre "b: ()"
 - [x] structfields.rs:    // @!has - //pre "c: usize"
 - [x] structfields.rs:    // @!has - //pre "// some fields omitted"
 - [x] structfields.rs:        // @!has - //pre "b: ()"
 - [x] issue-46767.rs:// @!has foo/index.html '//a/@href' './private/index.html'
 - [x] assoc-consts.rs:    // @!has - FOO_HIDDEN
 - [x] assoc-consts.rs:    // @!has - FOO_HIDDEN
 - [x] assoc-consts.rs:    // @!has assoc_consts/struct.Bar.html 'BAR_PRIVATE'
 - [x] assoc-consts.rs:    // @!has assoc_consts/struct.Bar.html 'BAR_HIDDEN'
 - [x] issue-53689.rs:// @!has - 'MyStruct'
 - [x] search-index-summaries.rs:// @!has - 'www.example.com'
 - [x] search-index-summaries.rs:// @!has - 'More Foo.'
 - [x] impl-everywhere.rs:// @!has foo/fn.foo.html '//section[@id="main"]//pre' "x: &\'x impl Foo"
 - [x] impl-everywhere.rs:// @!has foo/fn.foo.html '//section[@id="main"]//pre' "-> &\'x impl Foo {"
 - [x] impl-everywhere.rs:// @!has foo/fn.foo2.html '//section[@id="main"]//pre' "x: &\'x impl Foo"
 - [x] impl-everywhere.rs:// @!has foo/fn.foo2.html '//section[@id="main"]//pre' '-> impl Foo2 {'
 - [x] impl-everywhere.rs:// @!has foo/fn.foo_foo.html '//section[@id="main"]//pre' '-> impl Foo + Foo2 {'
 - [x] impl-everywhere.rs:// @!has foo/fn.foo2.html '//section[@id="main"]//pre' "x: &'x (impl Foo + Foo2)"
 - [x] issue-19190.rs:// @!has - '//*[@id="static_foo.v"]' 'fn static_foo()'
 - [x] issue-19190.rs:// @!has - '//*[@id="method.static_foo"]' 'fn static_foo()'
 - [x] deprecated-impls.rs:    // @!has - 'fn_def_def_with_doc full'
 - [x] deprecated-impls.rs:    // @!has - 'fn_empty_with_doc full'
 - [x] deprecated-impls.rs:    // @!has - 'fn_def_with full'
 - [x] deprecated-impls.rs:    // @!has - 'fn_def_def_with_doc full'
 - [x] issue-19190-3.rs:// @!has - '//*[@id="method.new"]' 'fn new() -> String'
 - [x] issue-19190-3.rs:// @!has - '//*[@id="method.static_baz"]' 'fn static_baz()'
 - [x] issue-19190-3.rs:// @!has - '//*[@id="method.static_baz"]' 'fn static_baz()'
 - [x] sidebar-items.rs:// @!has - '//*[@class="sidebar-links"]/a' 'waza'
 - [x] sidebar-items.rs:// @!has - '//*[@class="sidebar-links"]/a' 'waza'
 - [x] issue-27104.rs:// @!has - 'extern crate std'
 - [x] issue-27104.rs:// @!has - 'use std::prelude::'
 - [x] issue-13698.rs:// @!has issue_13698/struct.Foo.html '//*[@id="method.foo"]' 'fn foo'
 - [x] issue-13698.rs:// @!has issue_13698/struct.Foo.html '//*[@id="method.foo"]' 'fn bar'
 - [x] issue-41783.rs:// @!has - 'space'
 - [x] issue-41783.rs:// @!has - 'comment'
 - [x] trait-self-link.rs:// @!has trait_self_link/trait.Foo.html //a/@href ../trait_self_link/trait.Foo.html
 - [x] generic-impl.rs:// @!has foo/struct.Bar.html '//h3[@id="impl-ToString"]//code' 'impl<T> ToString for T'
 - [x] all.rs:// @!has foo/all.html 'private_module'
 - [x] issue-35169-2.rs:// @!has - '//*[@id="by_explicit_box.v"]' 'fn by_explicit_box(self: Box<Foo>)'
 - [x] issue-35169-2.rs:// @!has - '//*[@id="method.by_explicit_box"]' 'fn by_explicit_box(self: Box<Foo>)'
 - [x] issue-35169-2.rs:// @!has - '//*[@id="by_explicit_self_box.v"]' 'fn by_explicit_self_box(self: Box<Self>)'
 - [x] issue-35169-2.rs:// @!has - '//*[@id="method.by_explicit_self_box"]' 'fn by_explicit_self_box(self: Box<Self>)'
 - [x] issue-35169-2.rs:// @!has - '//*[@id="static_foo.v"]' 'fn static_foo()'
 - [x] issue-35169-2.rs:// @!has - '//*[@id="method.static_foo"]' 'fn static_foo()'
 - [x] doc-cfg.rs:// @!has - '//*[@id="main"]/*[@class="stability"]/*[@class="stab portability"]' ''
 - [x] inline_local/glob-private.rs:// @!has - "mod1"
 - [x] inline_local/glob-private.rs:// @!has - "Mod1Private"
 - [x] inline_local/glob-private.rs:// @!has - "mod2"
 - [x] inline_local/glob-private.rs:// @!has - "Mod2Private"
 - [x] inline_local/glob-private.rs:// @!has foo/struct.Mod1Private.html
 - [x] inline_local/glob-private.rs:// @!has foo/struct.Mod2Private.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod1/index.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod1/struct.Mod1Private.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod1/struct.Mod2Public.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod1/struct.Mod2Private.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod1/mod2/index.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod1/mod2/struct.Mod2Private.html
 - [x] inline_local/glob-private.rs:// @!has-dir foo/mod2
 - [x] inline_local/glob-private.rs:// @!has foo/mod2/index.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod2/struct.Mod2Public.html
 - [x] inline_local/glob-private.rs:// @!has foo/mod2/struct.Mod2Private.html
 - [x] inline_local/hidden-use.rs:// @!has - 'private'
 - [x] inline_local/hidden-use.rs:// @!has - 'Foo'
 - [x] inline_local/hidden-use.rs:// @!has hidden_use/struct.Foo.html
 - [x] inline_local/glob-extern-no-defaults.rs:// @!has - "private_fn"
 - [x] inline_local/glob-extern-no-defaults.rs:// @!has foo/fn.private_fn.html
 - [x] inline_local/issue-32343.rs:// @!has issue_32343/struct.Foo.html
 - [x] inline_local/issue-32343.rs:// @!has - '//code/a' 'Foo'
 - [x] inline_local/issue-32343.rs:// @!has issue_32343/struct.Bar.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has - "Mod1Private"
 - [x] inline_local/glob-private-no-defaults.rs:// @!has - "mod2"
 - [x] inline_local/glob-private-no-defaults.rs:// @!has - "Mod2Private"
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/struct.Mod1Private.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/struct.Mod2Private.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has - "Mod2Public"
 - [x] inline_local/glob-private-no-defaults.rs:// @!has - "Mod2Private"
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/mod1/struct.Mod2Public.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/mod1/struct.Mod2Private.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/mod2/index.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/mod2/struct.Mod2Public.html
 - [x] inline_local/glob-private-no-defaults.rs:// @!has foo/mod2/struct.Mod2Private.html
 - [x] inline_local/glob-extern.rs:// @!has - "mod1"
 - [x] inline_local/glob-extern.rs:// @!has - "private_fn"
 - [x] inline_local/glob-extern.rs:// @!has foo/fn.private_fn.html
 - [x] inline_local/glob-extern.rs:// @!has foo/mod1/index.html
 - [x] inline_local/glob-extern.rs:// @!has foo/mod1/fn.private_fn.html
 - [x] inline_local/please_inline.rs:    // @!has - 'pub use foo::'
 - [x] inline_local/please_inline.rs:    // @!has please_inline/b/struct.Foo.html
 - [x] inline_cross/hidden-use.rs:// @!has - 'rustdoc_hidden'
 - [x] inline_cross/hidden-use.rs:// @!has - 'Bar'
 - [x] inline_cross/hidden-use.rs:// @!has hidden_use/struct.Bar.html
 - [x] inline_cross/inline_hidden.rs:// @!has - '//a/@title' 'Foo'
 - [x] inline_cross/assoc-items.rs:// @!has - 'PrivateConst'
 - [x] inline_cross/assoc-items.rs:// @!has - 'private_method'
 - [x] inline_cross/cross-glob.rs:// @!has cross_glob/index.html '//code' 'pub use inner::*;'
 - [x] inline_cross/macro-vis.rs:// @!has - '//pre' 'some_macro'
 - [x] inline_cross/macro-vis.rs:// @!has macro_vis/macro.other_macro.html
 - [x] inline_cross/macro-vis.rs:// @!has macro_vis/index.html '//a/@href' 'macro.other_macro.html'
 - [x] inline_cross/macro-vis.rs:// @!has - '//code' 'pub use qwop::other_macro;'
 - [x] inline_cross/macro-vis.rs:// @!has macro_vis/macro.super_macro.html
 - [x] inline_cross/issue-31948.rs:// @!has - '//*[@class="impl"]//code' 'Bar for'
 - [x] inline_cross/issue-31948.rs:// @!has - '//*[@class="impl"]//code' 'Qux for'
 - [x] inline_cross/issue-31948.rs:// @!has - '//code' 'for Wibble'
 - [x] inline_cross/issue-31948.rs:// @!has - '//code' 'for Wobble'
 - [x] inline_cross/issue-31948.rs:// @!has - '//code' 'for Wibble'
 - [x] inline_cross/issue-31948.rs:// @!has - '//code' 'for Wobble'
 - [x] inline_cross/issue-31948.rs:// @!has issue_31948/trait.Bar.html
 - [x] inline_cross/issue-31948.rs:// @!has issue_31948/trait.Qux.html
 - [x] inline_cross/issue-31948.rs:// @!has issue_31948/struct.Wibble.html
 - [x] inline_cross/issue-31948.rs:// @!has issue_31948/struct.Wobble.html
 - [x] inline_cross/issue-31948-1.rs:// @!has - '//*[@class="impl"]//code' 'Bar for'
 - [x] inline_cross/issue-31948-1.rs:// @!has - '//*[@class="impl"]//code' 'Qux for'
 - [x] inline_cross/issue-31948-1.rs:// @!has - '//code' 'for Wibble'
 - [x] inline_cross/issue-31948-1.rs:// @!has - '//code' 'for Wibble'
 - [x] inline_cross/issue-31948-1.rs:// @!has issue_31948_1/trait.Bar.html
 - [x] inline_cross/issue-31948-1.rs:// @!has issue_31948_1/trait.Qux.html
 - [x] inline_cross/issue-28480.rs:// @!has -  '//a/@title' 'Hidden'
 - [x] inline_cross/issue-28480.rs:// @!has -  '//a/@title' 'Hidden'
 - [x] inline_cross/issue-31948-2.rs:// @!has - '//*[@class="impl"]//code' 'Bar for'
 - [x] inline_cross/issue-31948-2.rs:// @!has issue_31948_2/trait.Bar.html
 - [x] inline_cross/issue-31948-2.rs:// @!has issue_31948_2/trait.Woof.html
 - [x] inline_cross/issue-31948-2.rs:// @!has issue_31948_2/trait.Bark.html

It doesn't look like `@!matches` is used anywhere.

Don't try to promote already promoted out temporaries

fixes #53201

r? @EddyB

Remove `cargo new --edition` from release notes.

This was removed at the last minute (#55315, https://github.com/rust-lang/cargo/pull/6216).
Apologies for not catching this.

Keep resolved defs in path prefixes and emit them in save-analysis

Closes https://github.com/nrc/rls-analysis/issues/109

r? @EddyB or @petrochenkov

Primarily refactoring `(Ident, Option<NodeId>)` to `Segment`

FIxes https://github.com/rust-lang-nursery/rls/issues/1031

Requires adding path segments to the hir map

Rewrite the `UnconditionalRecursion` lint to use MIR

Part of #51002

r? @EddyB

Rollup of 22 pull requests

Successful merges:

 - #53507 (Add doc for impl From for Waker)
 - #53931 (Gradually expanding libstd's keyword documentation)
 - #54965 (update tcp stream documentation)
 - #54977 (Accept `Option<Box<$t:ty>>` in macro argument)
 - #55138 (in which unused-parens suggestions heed what the user actually wrote)
 - #55173 (Suggest appropriate syntax on missing lifetime specifier in return type)
 - #55200 (Documents `From` implementations for `Stdio`)
 - #55245 (submodules: update clippy from 5afdf8b7 to b1d03437)
 - #55247 (Clarified code example in char primitive doc)
 - #55251 (Fix a typo in the documentation of RangeInclusive)
 - #55253 (only issue "variant of the expected type" suggestion for enums)
 - #55254 (Correct trailing ellipsis in name_from_pat)
 - #55269 (fix typos in various places)
 - #55282 (Remove redundant clone)
 - #55285 (Do some copy editing on the release notes)
 - #55291 (Update stdsimd submodule)
 - #55296 (Set RUST_BACKTRACE=0 for rustdoc-ui/failed-doctest-output.rs)
 - #55306 (Regression test for #54478.)
 - #55328 (Fix doc for new copysign functions)
 - #55340 (Operands no longer appear in places)
 - #55345 (Remove is_null)
 - #55348 (Update RELEASES.md after destabilization of non_modrs_mods)

Failed merges:

r? @ghost

Backports the release notes update from stable to master.

r? @ghost

Remove is_null

It was confusingly named (`is_zero` would have been better, as someone pointed out somewhere but I forgot who or where), and it didn't even reliably test for "is this value 0 at run-time" because out-of-bounds pointers *can* be 0.

It's not used in rustc, and miri only really needs `is_null_ptr` and `to_bytes() == 0`, so let's just kill this method.

r? @oli-obk

Operands no longer appear in places

Fix an outdated comment.

Fix doc for new copysign functions

Thanks to @LukasKalbertodt for catching this. Addresses a comment raised in #55169 after it was merged.

Regression test for #54478.

This is a regression test for #54478.

I confirmed that it fails on:
rustdoc 1.30.0-beta.12 (96a22982 2018-10-04)
and passes on:
rustdoc 1.31.0-nightly (f99911a4 2018-10-23)

Fix #54478

Set RUST_BACKTRACE=0 for rustdoc-ui/failed-doctest-output.rs

This UI test is sensitive to backtrace output, so it should make sure
that backtraces are not enabled by the environment.

Update stdsimd submodule

Fixes a SSE2 bug. (#55249)

Do some copy editing on the release notes

I was reading through the release notes to find something and noticed
some small grammatical and consistency issues.

I'm happy to revert any of these changes if folks disagree with them!

Remove redundant clone

fix typos in various places

Correct trailing ellipsis in name_from_pat

r? @GuillaumeGomez

only issue "variant of the expected type" suggestion for enums

This suggestion (introduced in pull-request #43178 / eac74104) was being issued for one-field-struct expected types (in which case it is misleading and outright wrong), even though it was only intended for one-field enum-variants (most notably, `Some`).

Add a conditional to adhere to the original intent. (It would be possible to generalize to structs, but not obviously net desirable.) This adds a level of indentation, so the diff here is going to be
easier to read in [ignore-whitespace mode](https://github.com/rust-lang/rust/commit/b0d3d3b9?w=1).

Resolves #55250.

r? @pnkfelix

Fix a typo in the documentation of RangeInclusive

Clarified code example in char primitive doc

The example was not as clear as it could be because it was making an assumption about the structure of the data in order to multiply the number of elements in the slice by the item size. This change demonstrates the idea more straightforwardly, without needing a calculation, by just comparing the size of the slices.

submodules: update clippy from 5afdf8b7 to b1d03437

Just a routine update.

Changes:
````
new_ret_no_self: add sample from #3313 to Known Problems section.
Support multiline comments and hopefully fix panic
Check for comments in collapsible ifs
Resolve ICE in needless range loop lint
RIIR update_lints: Update changelog links
Rename if_let_redundant_pattern_matching to redundant_pattern_matching
Add lint for redundant pattern matching for explicit return boolean
Fix issue #3322: reword help message for len_zero
Simplify manual_memcpy suggestion in some cases
Fix dogfood
Update known problems for unnecessary_fold
RIIR update_lints: Replace lint count in README.md
Rename `active_lints` to `usable_lints`
Add comment on WalkDir vs. fs::read_dir
sort_by -> sort_by_key
Some more documentation for clippy_dev
Use `WalkDir` to also gather from subdirectories
Avoid linting `boxed_local` on trait implementations.
Website: Make lint categories linkable
Restore clippy_dummy's placeholder name
Swap order of methods in `needless_range_loop` suggestion in some cases
Revert "Exclude pattern guards from unnecessary_fold lint"
Exclude pattern guards from unnecessary_fold lint
````

Documents `From` implementations for `Stdio`

This PR solves part of #51430 by adding a basic summary and an example to each `impl From` inside `process` module (`ChildStdin`, `ChildStdout`, `ChildStderr`, `File`).

It does not document if the conversions allocate memory and how expensive they are.