Auto merge of #132196 - compiler-errors:probe_ty_param_bounds, r=petrochenkov

Some where clause lowering simplifications

Rename `PredicateFilter::SelfThatDefines` to `PredicateFilter::SelfTraitThatDefines` to make it clear that it's only concerned with converting *traits*, and make it do a bit less work when converting bounds.

Also, make the predicate filter matching in `probe_ty_param_bounds_in_generics` explicit, and simply the args it receives a bit.

Author: bors