This is in preparation for removing `ArcBorrow` and making `WithRef`
public.

Suggested-by: Björn Roy Baron <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>

With GATs, we don't need a separate type to represent a borrowed object
with a refcount, we can just use Rust's regular shared borrowing. In
this case, we use `&WithRef<T>` instead of `ArcBorrow<'_, T>`.

Co-developed-by: Boqun Feng <[email protected]>
Signed-off-by: Boqun Feng <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>