Auto merge of #85755 - b-naber:unexpected_concrete_region, r=nikomatsakis

Auto merge of #85755 - b-naber:unexpected_concrete_region, r=nikomatsakis

Replace parent substs of associated types with inference vars in borrow checker

Fixes https://github.com/rust-lang/rust/issues/83190
Fixes https://github.com/rust-lang/rust/issues/78450

When we normalize an associated type that refers to an opaque type, it can happen that the substs of the associated type do not occur in the projection (they are parent substs). We previously didn't replace those substs with inference vars, which left a concrete region after all regions should have already been replaced with inference vars and triggered a `delay_span_bug`. After we normalize the opaque type, we now try to replace any remaining concrete regions with inference vars.