slice: Stabilize IterMut::as_slice. Much like #72584. As per #58957 there's no blocker for this, and I wanted to use this today :-) Closes #58957
slice: Stabilize IterMut::as_slice. Much like #72584. As per #58957 there's no blocker for this, and I wanted to use this today :-) Closes #58957