Rollup merge of rust-lang#91323 - RalfJung:assert-type, r=oli-obk

CTFE: support assert_zero_valid and assert_uninit_valid

This ensures the implementation of all three type-based assert_ intrinsics remains consistent in Miri.

`assert_inhabited` recently got stabilized in rust-lang#90896 (meaning stable `const fn` can call it), so do the same with these other intrinsics.

Cc ```@rust-lang/wg-const-eval```

Author: JohnTitor

core/src/intrinsics.rs

@@ -860,12 +860,14 @@ extern "rust-intrinsic" {
     /// zero-initialization: This will statically either panic, or do nothing.
     ///
     /// This intrinsic does not have a stable counterpart.
+    #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
     pub fn assert_zero_valid<T>();
 
     /// A guard for unsafe functions that cannot ever be executed if `T` has invalid
     /// bit patterns: This will statically either panic, or do nothing.
     ///
     /// This intrinsic does not have a stable counterpart.
+    #[rustc_const_unstable(feature = "const_assert_type2", issue = "none")]
     pub fn assert_uninit_valid<T>();
 
     /// Gets a reference to a static `Location` indicating where it was called.