Fix #53525  - Unify E0243, E0244, E0087, E0088, E0089, and E0090 into E0107

Fix #53525

This pr merges all errors related to too many or too few generic arguments in types and functions. E0243, E0244, E0087, E0088, E0089, E0090 errors will no longer be emitted and E0107 will be used instead.

Stablize Iterator::find_map

Stabilization PR for https://github.com/rust-lang/rust/issues/49602

Tidy CFTE/MIRI

Fixes #53596

Search a substring instead of start of string in rustdoc search

Fixes #49762.

r? @QuietMisdreavus

MIR: support user-given type annotations on fns, structs, and enums

This branch adds tooling to track user-given type annotations on functions, structs, and enum variant expressions. The user-given types are passed onto NLL which then enforces them.

cc #47184 — not a complete fix, as there are more cases to cover

r? @EddyB
cc @rust-lang/wg-compiler-nll

Fix compile panic on non existent type return

Reverted the change https://github.com/rust-lang/rust/commit/28a76a90009d605349babcd2755962ab93913327#diff-4ed25c00aceb84666fca639cf8101c7cL1069 which was panicking when returning a type that cannot be found in the current scope and added testing for the compile error.

For example:
```rust
fn addition() -> Wrapper<impl A> {}
```
Where Wrapper is undefined in the scope.

the 3 is because the type arguments are in the 3rd position

Rollup of 16 pull requests

Successful merges:

 - #53311 (Window Mutex: Document that we properly initialize the SRWLock)
 - #53503 (Discourage overuse of mem::forget)
 - #53545 (Fix #50865: ICE on impl-trait returning functions reaching private items)
 - #53559 (add macro check for lint)
 - #53562 (Lament the invincibility of the Turbofish)
 - #53563 (use String::new() instead of String::from(""), "".to_string(), "".to_owned() or "".into())
 - #53592 (docs: minor stylistic changes to str/string docs)
 - #53594 (Update RELEASES.md to include clippy-preview)
 - #53600 (Fix a grammatical mistake in "expected generic arguments" errors)
 - #53614 (update nomicon and book)
 - #53617 (tidy: Stop requiring a license header)
 - #53618 (Add missing fmt examples)
 - #53636 (Prefer `.nth(n)` over `.skip(n).next()`.)
 - #53644 (Use SmallVec for SmallCStr)
 - #53664 (Remove unnecessary closure in rustc_mir/build/mod.rs)
 - #53666 (Added rustc_codegen_llvm to compiler documentation.)

Added rustc_codegen_llvm to compiler documentation.

Fixes #51737.

Fix #50865: ICE on impl-trait returning functions reaching private items

Adds a test case as suggested in #50865, and implements @petrochenkov's suggestion. Fixes #50865.

Impl-trait-returning functions are marked under a new (low) access level, which they propagate rather than `AccessLevels::Reachable`. `AccessLevels::is_reachable` returns false for such items (leaving stability analysis unaffected), these items may still be visible to the lints phase however.

Stabilize 'attr_literals' feature.

RFC Issue: rust-lang/rfcs#1559
Tracking Issue: rust-lang/rust#34981

Reference PR: https://github.com/rust-lang-nursery/reference/pull/388.

emitted" messages to the others.

Remove unnecessary closure in rustc_mir/build/mod.rs

Fixes #53608

Use SmallVec for SmallCStr

This reuses the awesome optimizations from Servo's `SmallVec` to speed up `SmallCStr`.

Prefer `.nth(n)` over `.skip(n).next()`.

Found by clippy.

Add missing fmt examples

r? @QuietMisdreavus

tidy: Stop requiring a license header

Previously approved in rust-lang/rust#43498 ; update tidy to match.

update nomicon and book

Fix a grammatical mistake in "expected generic arguments" errors

r? @EddyB

Update RELEASES.md to include clippy-preview

[Rendered](https://github.com/rust-lang/rust/blob/Aaronepower-patch-1/RELEASES.md#misc)

r? @Mark-Simulacrum

docs: minor stylistic changes to str/string docs

std::string::String.repeat(): slightly rephrase to be more in-line with other descriptions.

add ticks around a few keywords in other descriptions.

Address two regressions

Remove assert checking that expansion data is immutable until I have time to investigate why it's firing, cc https://github.com/rust-lang/rust/issues/52363
Turn the error for module-relative access to macro-expanded `macro_export` macros into a deprecation lint, closes https://github.com/rust-lang/rust/issues/53495