Rollup merge of #80874 - jyn514:intra-doc-docs, r=Manishearth

Update intra-doc link documentation to match the implementation

r? `@Manishearth`
cc `@camelid` `@m-ou-se`

Relevant PRs:
- https://github.com/rust-lang/rust/pull/74489
- https://github.com/rust-lang/rust/pull/80181
- https://github.com/rust-lang/rust/pull/76078
- https://github.com/rust-lang/rust/pull/77519
- https://github.com/rust-lang/rust/pull/73101

Relevant issues:
- https://github.com/rust-lang/rust/issues/78800
- https://github.com/rust-lang/rust/issues/77200
- https://github.com/rust-lang/rust/issues/77199 / https://github.com/rust-lang/rust/issues/54191/

I haven't documented things that I consider 'just bugs', like https://github.com/rust-lang/rust/issues/77732, but I have documented features that aren't implemented, like https://github.com/rust-lang/rust/issues/78800.