Rollup merge of #145325 - clarfonthey:cast-init, r=scottmcm

Add `cast_init` and `cast_uninit` methods for pointers

ACP: rust-lang/libs-team#627
Tracking issue: rust-lang/rust#145036

This includes an incredibly low-effort search to find uses that could be switched to using these methods. I only searched for `cast::<\w>` and `cast::<MaybeUninit` because there would otherwise be way too much to look through, and I also didn't modify anything inside submodules/subtrees.

Author: Kobzol