Rollup merge of #149102 - bend-n:maybe_uninit_slice, r=joboet

stabilize maybe_uninit_slice

Tracking issue: rust-lang/rust#63569
Closes: rust-lang/rust#63569
FCP completed: rust-lang/rust#63569 (comment)

Removes:
```rs
pub const fn slice_as_ptr(this: &[MaybeUninit<T>]) -> *const T;
pub const fn slice_as_mut_ptr(this: &mut [MaybeUninit<T>]) -> *mut T;
```

Author: matthiaskrgr