wayland-surface: Rework construction / destruction yet again

This time, to make way for MetaSurfaceActorEmpty. This also fixes
destroy effects as a side effect. It still has issues if we try
to re-assign an actor that's already toplevel (e.g. somebody
re-popping up a menu that's already being destroyed), but this
will be fixed soon.

The idea here is that MetaWindowActor will do the unparenting of
the surface actor when it itself is destroyed. To prevent bad issues
with picking, we only make the surface actor reactive when it's
toplevel.

src/wayland/meta-wayland-surface.h

@@ -118,6 +118,7 @@ MetaWaylandSurface *meta_wayland_surface_create (MetaWaylandCompositor *composit
 						 guint32                id,
 						 guint32                version);
 
+void                meta_wayland_surface_make_toplevel (MetaWaylandSurface *surface);
 void                meta_wayland_surface_window_unmanaged (MetaWaylandSurface *surface);
 
 void                meta_wayland_surface_configure_notify (MetaWaylandSurface *surface,