rustdoc: improve appearance of source page navigation bar

This commit changes things so that the search bar is exactly centered between the top of the page and the top of the source code content area.

Preview: https://notriddle.com/notriddle-rustdoc-demos/source-page-header/src/std/lib.rs.html

## Before

![image](https://user-images.githubusercontent.com/1593513/197053420-02a64627-48ed-4bb6-9363-a1863d47b092.png)

## After

![image](https://user-images.githubusercontent.com/1593513/197053355-bd6149f9-0f5c-47da-aeb7-590b5eecb5da.png)

Fixup a few tests needing asm support

Account for hygiene in typo suggestions, and use them to point to shadowed names

Fixes https://github.com/rust-lang/rust/issues/97459

r? `@estebank`

translation: doc comments with derives, subdiagnostic-less enum variants, more derive use

- Adds support for `doc` attributes in the diagnostic derives so that documentation comments don't result in the derive failing.
- Adds support for enum variants in the subdiagnostic derive to not actually correspond to an addition to a diagnostic.
- Made use of the derive in more places in the `rustc_ast_lowering`, `rustc_ast_passes`, `rustc_lint`, `rustc_session`, `rustc_infer` - taking advantage of recent additions like eager subdiagnostics, multispan suggestions, etc.

cc #100717

Filtering spans when emitting json

According to the issue #102902, we shouldn't emit spans which have an empty span and no suggested replacement.

Elaborate supertrait bounds when triggering `unused_must_use` on `impl Trait`

Given `impl Trait`, if one of its supertraits has a `#[must_use]`, then trigger the lint. This means that, for example, `-> impl ExactSizeIterator` also triggers the `must_use` on `trait Iterator`, which fixes #102183.

This might need `@rust-lang/lang` sign-off, since it changes the behavior of the lint, so cc'ing them.

Mark `std::os::wasi::io::AsFd` etc. as stable.

io_safety was stabilized in Rust 1.63, so mark the io_safety exports in `std::os::wasi::io` as stable.

Fixes #103306.

Rollup of 9 pull requests

Successful merges:

 - #103221 (Fix `SelfVisitor::is_self_ty` ICE)
 - #103230 (Clarify startup)
 - #103281 (Adjust `transmute{,_copy}` to be clearer about which of `T` and `U` is input vs output)
 - #103288 (Fixed docs typo in `library/std/src/time.rs`)
 - #103296 (+/- shortcut now only expand/collapse, not both)
 - #103297 (fix typo)
 - #103313 (Don't label `src/test` tests as `A-testsuite`)
 - #103315 (interpret: remove an incorrect assertion)
 - #103319 (Improve "`~const` is not allowed here" message)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Improve "`~const` is not allowed here" message

r? `@oli-obk`

interpret: remove an incorrect assertion

This fixes an ICE in Miri, [reported](https://rust-lang.zulipchat.com/#narrow/stream/269128-miri/topic/SwitchInt.20with.20no.20targets.3F) by `@saethlin.` The faulty assertion was introduced by https://github.com/rust-lang/rust/commit/432535da2b5144d467056efcfa6864d35ba2de0f, when a previously correct assertion checking that the `otherwise` target exists got replaced by this assertion checking that at least one more target beyond `otherwise` exists.

Sadly we don't have a small reproducer so I don't think we can easily add a testcase.

Don't label `src/test` tests as `A-testsuite`

Nearly every PR modifies `src/test`; A-testsuite is meant to be for things affecting the test runners themselves.

cc https://github.com/rust-lang/rust/pull/103204#discussion_r1000868781

r? `@jyn514`

fix typo

+/- shortcut now only expand/collapse, not both

Fixes https://github.com/rust-lang/rust/issues/102772.

r? ```@notriddle```

Fixed docs typo in `library/std/src/time.rs`

* Changed comment from `Previous rust versions panicked when self was earlier than the current time.` to `Previous rust versions panicked when the current time was earlier than self.`
* Resolves #103282.

Adjust `transmute{,_copy}` to be clearer about which of `T` and `U` is input vs output

This is essentially a documentation-only change (although it does touch code in an irrelevant way).

Clarify startup

A small follow-up to #102769.

r? `@jyn514`

Fix `SelfVisitor::is_self_ty` ICE

Fixes #103202

This commit changes things so that the search bar is exactly centered between
the top of the page and the top of the source code content area.

linker: Fix weak lang item linking with combination windows-gnu + LLD + LTO

In https://github.com/rust-lang/rust/pull/100404 this logic was originally disabled for MSVC due to issues with LTO, but the same issues appear on windows-gnu with LLD because that LLD uses the same underlying logic as MSVC LLD, just with re-syntaxed command line options.

So this PR just disables it for LTO builds in general.

io_safety was stabilized in Rust 1.63, so mark the io_safety exports in
`std::os::wasi::io` as stable.

Fixes #103306.

Rollup of 6 pull requests

Successful merges:

 - #103197 (Stabilize proc_macro::Span::source_text)
 - #103251 (Fix item declaration highlighting)
 - #103262 (Adjusting test to needs-unwind, with linking issue)
 - #103268 (rustdoc: remove no-op CSS `nav.sub { font-size: 1rem }`)
 - #103272 (Remove extra spaces in docs)
 - #103276 (Erase regions before checking for `Default` in uninitialized binding error)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Fix the bug of next_point in source_map

There is a bug in `next_point`, the new span won't move to next position when be called in the first time.

For this reason, our current code is working like this:
1. When we really want to move to the next position, we called two times of `next_point`
2. Some code which use `next_point` actually done the same thing with `shrink_to_hi`

This fix make sure when `next_point` is called, span will move with the width at least 1, and also work correctly in the scenario of multiple bytes.

Ref: https://github.com/rust-lang/rust/pull/103140#discussion_r997710998

r? `@davidtwco`

Erase regions before checking for `Default` in uninitialized binding error

Fixes #103250

Remove extra spaces in docs

Removing some random extra spaces in the examples for `core::sync::atomic`.

r? `@thomcc`

rustdoc: remove no-op CSS `nav.sub { font-size: 1rem }`

This rule originated as a `font-size: 16px`, when body had `font-size: 13px` set in 4fd061c4.

It remained even when body's font size was bumped up to 16px, 4d5f4ff5, making the rule a no-op, and was carried forward when it was converted to 1rem in cc181204.

Adjusting test to needs-unwind, with linking issue

Test requires `needs-unwind` (see linked issue #103261)

Fix item declaration highlighting

Fixes https://github.com/rust-lang/rust/issues/103050.

As mentioned in the issue, https://github.com/rust-lang/rust/pull/102924 introduced this regression. This PR partially reverts it and adds a regression test.

r? `@notriddle`

Stabilize proc_macro::Span::source_text

Splits `proc_macro::Span::source_text` into a new feature gate and stabilizes it. The [FCP is complete](https://github.com/rust-lang/rust/issues/101991#issuecomment-1279393265).

```Rust
impl Span {
    pub fn source_text(&self) -> Option<String>;
}
```

Closes #101991

Deny hashing ty/re/ct inference variables

cc `@cjgillot` and https://github.com/rust-lang/rust/pull/102695#issuecomment-1275706528
r? `@lcnr`

best reviewed one commit at a time, mostly because the second commit that fixes `ClosureOutlivesRequirement` is mostly noise because of losing its `<'tcx>` lifetime parameter.