wayland: Add getter for the implicitly grabbed surface of a touch sequence

This will be used to implement the default MetaWaylandEventInterface at
MetaWaylandSeat.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3420>

src/wayland/meta-wayland-touch.c

@@ -637,6 +637,22 @@ meta_wayland_touch_get_press_coords (MetaWaylandTouch     *touch,
   return TRUE;
 }
 
+MetaWaylandSurface *
+meta_wayland_touch_get_surface (MetaWaylandTouch     *touch,
+                                ClutterEventSequence *sequence)
+{
+  MetaWaylandTouchInfo *touch_info;
+
+  if (!touch->touches)
+    return NULL;
+
+  touch_info = touch_get_info (touch, sequence, FALSE);
+  if (!touch_info || !touch_info->touch_surface)
+    return NULL;
+
+  return touch_info->touch_surface->surface;
+}
+
 static void
 meta_wayland_touch_init (MetaWaylandTouch *touch)
 {

src/wayland/meta-wayland-touch.h

@@ -73,3 +73,6 @@ gboolean meta_wayland_touch_get_press_coords (MetaWaylandTouch     *touch,
 
 gboolean meta_wayland_touch_can_popup        (MetaWaylandTouch *touch,
                                               uint32_t          serial);
+
+MetaWaylandSurface * meta_wayland_touch_get_surface (MetaWaylandTouch     *touch,
+                                                     ClutterEventSequence *sequence);