gdk: handle implicit touch grabs

gdk: handle implicit touch grabs

If the touch sequence happens on a window with GDK_TOUCH_MASK set,
a GdkTouchGrabInfo is created to back it up. Else a device grab is
only created if the sequence emulates the pointer.

If both a device and a touch grab are present on a window, the later
of them both is obeyed, Any grab on the device happening after a
touch grab generates grab-broken on all the windows an implicit
touch grab was going on.