This allows user to be in control of when scaling happens in the pipeline.
It can be plugged as an effect and scaling will be forced to happen in
the effect instead of in the compositor.
Without this, it would not be possible for users to, for example,
crop a video source before scaling to the target source size.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5735>
