Check signature WF when lowering MIR body Alternative to #137233. https://github.com/rust-lang/rust/pull/137233#issuecomment-2667879143 Fixes https://github.com/rust-lang/rust/issues/137186 We do this check in `mir_drops_elaborated_and_const_checked` and not during `mir_promoted` because that may result in borrowck cycles if WF requires looking into an opaque hidden type. This causes some TAIT tests to fail unnecessarily. r? lcnr try-job: test-various