Stabilize `const_maybe_uninit_zeroed` and `const_mem_zeroed` Make `MaybeUninit::zeroed` and `mem::zeroed` const stable. Newly stable API: ```rust // core::mem pub const unsafe fn zeroed<T>() ->; impl<T> MaybeUninit<T> { pub const fn zeroed() -> MaybeUninit<T>; } ``` This relies on features based around `const_mut_refs`. Per `@RalfJung,` this should be OK since we do not leak any `&mut` to the user. For this to be possible, intrinsics `assert_zero_valid` and `assert_mem_uninitialized_valid` were made const stable. Tracking issue: #91850 Zulip discussion: https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/topic/.60const_mut_refs.60.20dependents r? libs-api `@rustbot` label -T-libs +T-libs-api +A-const-eval cc `@RalfJung` `@oli-obk` `@rust-lang/wg-const-eval`