gdkwindow: Update cursor for tablet tools in the window

This check must be done explicitly on Wayland as the master device for
tablet tools differ from the Core Pointer. This ensures that whenever a
tablet tool is inside a window and the cursor is programmatically changed,
it will be visually updated too.

https://bugzilla.gnome.org/show_bug.cgi?id=785375

gdk/gdkwindow.c

@@ -6583,8 +6583,18 @@ gdk_window_set_cursor (GdkWindow *window,
 
       for (s = seats; s; s = s->next)
         {
+          GList *devices, *d;
+
           device = gdk_seat_get_pointer (s->data);
           gdk_window_set_cursor_internal (window, device, window->cursor);
+
+          devices = gdk_seat_get_slaves (s->data, GDK_SEAT_CAPABILITY_TABLET_STYLUS);
+          for (d = devices; d; d = d->next)
+            {
+              device = gdk_device_get_associated_device (d->data);
+              gdk_window_set_cursor_internal (window, device, window->cursor);
+            }
+          g_list_free (devices);
         }
 
       g_list_free (seats);