MetaScreen: Add tracking of whether there are fullscreen windows

Trying to track the fullscreen status outside of Mutter, as GNOME Shell
was doing previously, was very prone to errors, because Mutter has a
very tricky definition of when a window is set to be fullscreen and
*actually* acting like a fullscreen window.

 * Add meta_screen_get_monitor_in_fullscreen() and an
   ::in-fullscreen-changed signal. This allows an application to
   track when there are fullscreen windows on a monitor.

 * Do the computation of fullscreen status in a "later" function that
   runs after showing, so we properly take focus into account.

 * To get ordering of different phases right, add more values
   to MetaLaterType.

 * Add auto-minimization, similar to what was added to GNOME Shell
   earlier in this cycle - if a window is set to be fullscreen, but
   not actually fullscreen, minimize.

https://bugzilla.gnome.org/show_bug.cgi?id=649748

src/core/screen-private.h

@@ -46,6 +46,7 @@ struct _MetaMonitorInfo
   int number;
   MetaRectangle rect;
   gboolean is_primary;
+  gboolean in_fullscreen;
   XID output; /* The primary or first output for this crtc, None if no xrandr */
 };
 
@@ -117,6 +118,7 @@ struct _MetaScreen
   guint32 wm_cm_timestamp;
 
   guint work_area_later;
+  guint check_fullscreen_later;
 
   int rows_of_workspaces;
   int columns_of_workspaces;
@@ -201,6 +203,8 @@ void          meta_screen_get_natural_monitor_list (MetaScreen *screen,
 void          meta_screen_update_workspace_layout (MetaScreen             *screen);
 void          meta_screen_update_workspace_names  (MetaScreen             *screen);
 void          meta_screen_queue_workarea_recalc   (MetaScreen             *screen);
+void          meta_screen_queue_check_fullscreen  (MetaScreen             *screen);
+
 
 Window meta_create_offscreen_window (Display *xdisplay,
                                      Window   parent,