Emit errors/warns on some wrong uses of rustdoc attributes
This PR adds a few diagnostics:
- error if conflicting `#[doc(inline)]`/`#[doc(no_inline)]` are found
- introduce the `invalid_doc_attributes` lint (warn-by-default) which triggers:
- if a crate-level attribute is used on a non-`crate` item
- if `#[doc(inline)]`/`#[doc(no_inline)]` is used on a non-`use` item
The code could probably be improved but I wanted to get feedback first. Also, some of those changes could be considered breaking changes, so I don't know what the procedure would be? ~~And finally, for the warnings, they are currently hard warnings, maybe it would be better to introduce a lint?~~ (EDIT: introduced the `invalid_doc_attributes` lint)
Closes#80275.
r? `@jyn514`
fe62c6e295