We don't want to expose the GtkCrossingData struct, and manually
feeding events to event controllers is not something we want to
encourage, going forward.
... and use them.
Also, rename them from is/contains-pointer-focus to is/contains-pointer,
that's clear enough and not too long.
Finally, adapt the semantics of contains-pointer to mirror
GtkEventControllerKey::contains-focus. If is-pointer is set, so is
contains-pointer, they are not exclusive.
Which is what all users of this property wanted, too.
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.
