Rollup merge of #108672 - spastorino:new-rpitit-impl-side, r=compiler-errors

Feed queries on impl side for RPITITs when using lower_impl_trait_in_trait_to_assoc_ty

I've added a test for traits that were already working and what I think is probably the last bit of infrastructure work needed.
In following PRs I'm going to start adding things TDD style, tests and code that make it work.

r? `@compiler-errors`

Author: matthiaskrgr