Auto merge of #38766 - eddyb:less-fake-hir, r=arielb1

Stop creating fake HIR pattern nodes.

This replaces all the HIR patterns `rustc_const_eval` creates with the more appropriate HAIR equivalent.

The only place left that creates HIR nodes is the "explicit lifetimes in function signature" suggestion, which only creates type nodes while rebuilding the signature, but that is only in case of an error.

cc @arielb1