Do not convert copies of packed projections to moves. This code path was introduced in https://github.com/rust-lang/rust/pull/113758 After seeing https://rust-lang.zulipchat.com/#narrow/stream/136281-t-opsem/topic/Packed.20fields.20and.20in-place.20function.20argument.2Freturn.20passing, this may be UB, so should be disallowed. This should not appear in normally-built MIR, which introduces temporary copies for packed projections.