Setting four properties is more expensive than calling two C functions,
so move to set_origin()/set_size() calls for our ClutterActorBox
handling.
This gets us down to an average time of 2.1 ms spent in vfunc_allocate()
with 20 windows
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1743>