Add ptr::Pointee trait (for all types) and ptr::metadata function

RFC: https://github.com/rust-lang/rfcs/pull/2580

compiler/rustc_ty_utils/src/instance.rs

@@ -274,7 +274,8 @@ fn resolve_associated_item<'tcx>(
         traits::ImplSource::AutoImpl(..)
         | traits::ImplSource::Param(..)
         | traits::ImplSource::TraitAlias(..)
-        | traits::ImplSource::DiscriminantKind(..) => None,
+        | traits::ImplSource::DiscriminantKind(..)
+        | traits::ImplSource::Pointee(..) => None,
     })
 }