Auto merge of rust-lang#101454 - cjgillot:concat-binders, r=estebank

Do not overwrite lifetime binders for another HirId.

This PR makes higher-ranked bounds in where clauses a bit more principled.
We used to conflate `for<'a> T: Trait` with `(for<'a> T): Trait`.
This PR separates both binders.

This caused issued with fn types, which have their own binder, causing us to overwrite the predicates's binders with `fn`'s binders, ICEing.

Fixes rust-lang#98594

Author: bors