Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.
Traditionally (and on most backends) there's a single master pointer driven
by all pointing devices. The notable exception is Wayland though, where
master pointing devices are created per capability in the case of
pointer/touch, and one for each drawing tablet.
This function call makes it easy to access all these.
https://bugzilla.gnome.org/show_bug.cgi?id=790920
