Add `repeated_where_clause_or_trait_bound` lint
I thought I would try and scratch my own itch for #8674.
1. Is comparing the `Res` the correct way for ensuring we have the same trait?
2. Is there a way to get the spans for the bounds and clauses for suggestions?
I tried to use `GenericParam::bounds_span_for_suggestions` but it only gave me an empty span at the end of the spans.
I tried `WhereClause::span_for_predicates_or_empty_place` and it included the comma.
3. Is there a simpler way to get the trait names? I have used the spans of the traits because I didn't see a way to get it off the `Res` or `Def`.
changelog: Add ``[`repeated_where_clause_or_trait_bound`]`` lint.
9ebacd4874