This design decision was intentional and reflects the fact that we
cannot have inheritance tree 'linear' as before, since the base
interface is an abstract class without any data-members.
Also, fix a warning about size_t -> int implicit conversion.
Fixes: QTBUG-91866
Change-Id: Icbc73c22d8adf72bbd8949125d4404ea6da69c6d
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 1a7faeef94dcf6826c6ee564a1bfb31ebb952e56)