clutter: avoid redundant _clutter_paint_node_init_types()
This only needs to be initialized once but is in the hot path of creating new paint nodes (for which we create many). Instead, do this as part of the clutter_init() workflow to keep it out of the hot path.
This definitely needs to be double checked by someone who can verify that
getting the default backend is fine in clutter_init()
, but by my looks
and testing it seems completely fine. /CC @ebassi