gtk/range: Move button release handling to GtkGestureDrag

gtk/range: Move button release handling to GtkGestureDrag

Tracking it through the GtkGestureClick becomes a bit cumbersome for
handling of simultaneously pressed buttons. We can track ::stopped,
but that also emits for a number of situations where we want drag to
continue.

However, the GtkGestureDrag is grouped with the click gesture, and
knows better when to finish the drag gesture (not just because of a
button release), so hook drag and zoom mode finalization there.

Fixes: https://gitlab.gnome.org/GNOME/gtk/-/issues/3426