Gesture.group

Adds gesture to the same group than group_gesture. Gestures are by default isolated in their own groups.

When gestures are grouped, the state of #GdkEventSequences is kept in sync for all of those, so calling [gtk.gesture.Gesture.setSequenceState], on one will transfer the same value to the others.

Groups also perform an "implicit grabbing" of sequences, if a #GdkEventSequence state is set to #GTK_EVENT_SEQUENCE_CLAIMED on one group, every other gesture group attached to the same #GtkWidget will switch the state for that sequence to #GTK_EVENT_SEQUENCE_DENIED.