Add a signal for wlr_surface destruction on the wlr_surface that compositors
can listen to to remove the surface from their state.
Implement a listener for this in the example wl_compositor to remove the
surface from its internal list of surfaces.
Destroy the surface in the compositor destroy_surface callback given when the
surface resource was created.
Add a reference to the surface resource to the wlr_surface so a compositor can
find it in its list of resources upon wlr_resource destruction.
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