wayland: Update input device before repick

When a Wayland window is mapped or unmapped, the Wayland compositor is
expected to send the coorespoindign `wl_pointer` enter/leave events to
the affected clients.

To do so, mutter calls `meta_wayland_compositor_repick()` which
eventually calls `meta_wayland_pointer_repick()` and
`repick_for_event()`.

If pointer input device has not been updated yet, the old clutter actor
is picked and no enter/leave event is emitted.

Make sure we update the pointer input device prior to do the repick to
get the actual `ClutterActor` under the pointer.

Closes: https://gitlab.gnome.org/GNOME/mutter/issues/1016
https://gitlab.gnome.org/GNOME/mutter/merge_requests/1026

src/wayland/meta-wayland-pointer.c

@@ -1028,6 +1028,7 @@ meta_wayland_pointer_start_popup_grab (MetaWaylandPointer      *pointer,
 void
 meta_wayland_pointer_repick (MetaWaylandPointer *pointer)
 {
+  clutter_input_device_update (pointer->device, NULL, FALSE);
   repick_for_event (pointer, NULL);
 }