gtk: Use versioned deprecations

This patch changes all uses of GDK_DEPRECATED(_FOR) in gtk headers
by the versioned variants, GDK_DEPRECATED_IN_3_x(_FOR). At the same
time, we add GDK_AVAILABLE_IN_3_x annotations for all API additions
in 3.2 and 3.4.

gtk/gtkoverlay.h

@@ -68,9 +68,11 @@ struct _GtkOverlayClass
   void (*_gtk_reserved8) (void);
 };
 
+GDK_AVAILABLE_IN_3_2
 GType      gtk_overlay_get_type    (void) G_GNUC_CONST;
-
+GDK_AVAILABLE_IN_3_2
 GtkWidget *gtk_overlay_new         (void);
+GDK_AVAILABLE_IN_3_2
 void       gtk_overlay_add_overlay (GtkOverlay *overlay,
                                     GtkWidget  *widget);