This is one of the behaviors we no longer allow in NLL. Since it can
lead to undefined behavior, I think it's definitely worth making it a
hard error without waiting to turn off migration mode (#58781).
Closes#60450.
My ulterior motive here is making it impossible to leave variables
partially initialized across a yield (see discussion at #63035), so
tests are included for that.
Don't stop evaluating due to errors before borrow checking
r? @oli-obk
Fix#60005. Follow up to #59903. Blocked on #53708, fixing the ICE in `src/test/ui/consts/match_ice.rs`.
