MetaCursorTracker: add methods for setting the cursor visibility

clutter_stage_show_cursor()/hide_cursor() only works in the X11
backend (where someone else is in charge of showing the cursor),
and even then, it has confusing effects when running nested wayland,
so an abstraction layer is needed.

https://bugzilla.gnome.org/show_bug.cgi?id=707474

src/core/meta-cursor-tracker.c

@@ -426,7 +426,7 @@ meta_cursor_tracker_paint (MetaCursorTracker *tracker)
 {
   g_assert (meta_is_wayland_compositor ());
 
-  if (tracker->sprite == NULL)
+  if (tracker->sprite == NULL || tracker->is_showing == FALSE)
     return;
 
   /* FIXME: try to use a DRM cursor when possible */
@@ -513,3 +513,29 @@ meta_cursor_tracker_get_pointer (MetaCursorTracker   *tracker,
   else
     get_pointer_position_gdk (x, y, (int*)mods);
 }
+
+void
+meta_cursor_tracker_set_pointer_visible (MetaCursorTracker *tracker,
+                                         gboolean           visible)
+{
+  if (visible == tracker->is_showing)
+    return;
+  tracker->is_showing = visible;
+
+  if (meta_is_wayland_compositor ())
+    {
+      MetaWaylandCompositor *compositor;
+
+      compositor = meta_wayland_compositor_get_default ();
+      meta_cursor_tracker_queue_redraw (tracker, compositor->stage);
+    }
+  else
+    {
+      if (visible)
+        XFixesShowCursor (tracker->screen->display->xdisplay,
+                          tracker->screen->xroot);
+      else
+        XFixesHideCursor (tracker->screen->display->xdisplay,
+                          tracker->screen->xroot);
+    }
+}