This adds a signal that's emitted whenever a wayland surface is damaged
that allows sub-classes to override the default handler to change
how clipped redraws are queued if the sub-class doesn't simply draw
a rectangle. The signal can also be used just to track damage.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
Reviewed-by: Emmanuele Bassi <ebassi@linux.intel.com>
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