Rollup merge of #142275 - aDotInTheVoid:gen-ty-of, r=fmease

rustdoc: Refractor `clean_ty_generics`

Refactoring towards rust-lang/rust#142226

[Zulip Discussion](https://rust-lang.zulipchat.com/#narrow/channel/266220-t-rustdoc/topic/Why.20sometimes.20.60predicates_of.60.20.28vs.20.60explicit_predicates_.2E.2E.2E/near/523182529)

The old `clean_ty_generics` was almost always called with the same args, so rename it to `clean_ty_generics_inner`, and add a new wrapper that generates those args from a `DefId`. Having this be the main entrypoint to `clean_ty_generics` should make it easier to start calling `inferred_outlives_of` rust-lang/rust#142264 (comment) (and is more readable even if we don't)

Also, replaces all calls in rustdoc to `tcx.predicates_of` to `tcx.explicit_predicates_of`, which lets us remove `filter_non_trait_generics`

r? ```@fmease```

Author: fmease