This gives greater control to the callers on the place where a grab is being
activated, this may make a difference in the handling of crossing events
triggered through it, e.g. by having callers rely on having already obtained
a ClutterGrab prior to handling the resulting effects.

The "input only" grab has also been turned inactive by default, in order to
to have the ClutterGrab pointer available for checks at the MetaWaylandEventHandler
focus changing methods triggered through grab activation.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/3463
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3747>