Make clutter_actor_allocate_preferred_size() convenient to use from
layout managers by not "automatically" honouring the fixed position of
the actor, but instead allowing to pass a position to allocate the
actor at.
This way we can move the handling of fixed positions to
ClutterFixedLayout, the layout manager which is responsible for
allocating actors using fixed positions.
This also makes clutter_actor_allocate_preferred_size() more similar to
clutter_actor_allocate_available_size().
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1310
In cogl use cogl-config.h and in clutter use clutter-build-config.h. We
can't use clutter-config.h in clutter because its already used and
installed.
https://bugzilla.gnome.org/show_bug.cgi?id=768976
