Check def id before calling `match_projection_projections`
When I "inlined" `assemble_candidates_from_predicates` into `for_each_item_bound` in #120584, I forgot to copy over the check that actually made sure the def id of the candidate was equal to the def id of the obligation. This means that we normalize goal a bit too often even if it's not productive to do so.
This PR adds that def id check back.
Fixes#123448
8d490e33ad