Generalize NonNull::from_raw_parts per ACP362

I did the raw pointers in 125701, but apparently forgot `NonNull`.

library/core/src/ptr/non_null.rs

@@ -251,7 +251,7 @@ impl<T: ?Sized> NonNull<T> {
     #[unstable(feature = "ptr_metadata", issue = "81513")]
     #[inline]
     pub const fn from_raw_parts(
-        data_pointer: NonNull<()>,
+        data_pointer: NonNull<impl super::Thin>,
         metadata: <T as super::Pointee>::Metadata,
     ) -> NonNull<T> {
         // SAFETY: The result of `ptr::from::raw_parts_mut` is non-null because `data_pointer` is.