We query the transformed position and size of the popupMenu before actually showing
it which results into wrong positioning, when displaying it for the first time.
In case of the statusMenu this can even result into it being offscreen.
https://bugzilla.gnome.org/show_bug.cgi?id=621385
Add _st_actor_contains() in st-private for use within St, and
monkey-patch in a Clutter.Actor.contains() for use by javascript, and
then replace all the duplicate implementations with one or the other
of those.
https://bugzilla.gnome.org/show_bug.cgi?id=621197
