Detect when paths in src/utils/path.rs become outdated

[Aaron1011]

Clippy lists a lot of different paths in https://github.com/rust-lang/rust-clippy/blob/084b203988e04bcf89d3b2d6bbc77b65ecfab553/clippy_lints/src/utils/paths.rs, which are represented as strings. If one of these becomes invalid due to a compiler refactoring, Clippy will continue to compile - however, the behavior of lints may change, since the path will never match anything.

It would be useful to validate that all of the paths are valid (if the crate at the beginning of the path is loaded). I'm not sure how difficult this would be - I think we would need access to the resolver before we run any lints.

I came across this in rust-lang/rust#75534 - I moved the rustc Lint type, which caused an internal clippy lint to stop firing.

[ebroto]

Duplicate of #6047

FYI #6244 partially addressed this, but the dogfood tests don't run in the rustc repo (I guess because it takes some time), so we need to find a way to check those paths, ideally without duplication.