Auto merge of #131840 - compiler-errors:impossible-maybe, r=lcnr

Dont consider predicates that may hold as impossible in `is_impossible_associated_item`

Use infer vars to account for ambiguities when considering if methods are impossible to instantiate for a given self type. Also while we're at it, let's use the new trait solver instead of `evaluate` since this is used in rustdoc.

r? lcnr
Fixes #131839

Author: bors