don't skip inference for type in `offset_of!` Fixes https://github.com/rust-lang/rust/issues/111678 by no longer skipping inference on the type in `offset_of!`. Simply erasing the regions the during writeback isn't enough and can cause ICEs. A test case for this is included. This reverts https://github.com/rust-lang/rust/pull/111661, because it becomes redundant, since inference already erases the regions.