We're moving keeping track of input devices and their associated actors
out of ClutterInputDevice, this commit basically adds replacements for
clutter_input_device_update() and clutter_input_device_set_actor() to
clutter-main and shuffles the internals of those functions around a bit
for clarity.
clutter_stage_update_device() is made available in clutter-mutter.h
because we need to update the actor of input devices not only from
ClutterStage (when repicking after relayout), but also from
MetaWaylandPointer (inside meta_wayland_pointer_repick()).
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1633>
a9a9d27ead