surface-role-cursor: Send frame callbacks for backend handled cursors

For backend handled cursors, if nothing else changes on the clutter
stage, we end up not sending out frame callbacks since clutter doesn't
draw a new frame.

To fix this, we'll keep cursor surfaces' frame callbacks separate from
other surfaces' and trigger them from the new
MetaCursorRenderer::cursor-painted signal which handles both software
and hardware cursors.

https://bugzilla.gnome.org/show_bug.cgi?id=749913