Auto merge of #116233 - DaniPopes:stabilize-const_maybe_uninit_assume_init_read, r=dtolnay

Stabilize `const_maybe_uninit_assume_init_read`

AFAICT the only reason this was not included in the `maybe_uninit_extra` stabilization was because `ptr::read` was unstable (rust-lang/rust#92768 (comment)), which has since been stabilized in 1.71.

Needs a separate FCP from the [original `maybe_uninit_extra` one](rust-lang/rust#63567 (comment)).

Tracking issue: #63567

Author: bors