clutter-actor: Cull actors that don't intersect the redraw clip

Previously we only culled actors that didn't intersect the bounding box of the redraw clip. Now we also cull those whose paint volume bounds don't intersect the arbitrary shape of the redraw clip.

This was inspired by the activities overview where idle windows and workspace previews were being needlessly repainted. In that particular case this yields more than 10% reduction in render time. But it probably helps in other situations too.