Rollup merge of #108669 - Nilstrieb:query-my-uninitness, r=compiler-errors

Allow checking whether a type allows being uninitialized

This is useful for clippy ([rust-lang/clippy#10407](https://github.com/rust-lang/rust-clippy/issues/10407)) and for the future `MaybeUninit::assume_init` panics (#100423).

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -444,6 +444,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                             "aborted execution: attempted to leave type `{}` uninitialized, which is invalid",
                             ty
                         ),
+                        ValidityRequirement::Uninit => bug!("assert_uninit_valid doesn't exist"),
                     };
 
                     M::abort(self, msg)?;