compositor: Don't lift planes out of scene graph entirely

When we lift planes entirely out of the scene graph, paint node visibility
calculations become "per plane". This means that when we lift something
onto a paint node, anything beneath it will be redrawn in response to
client side damage even if the lower surfaces are occluded.

Instead, keep the scene graph together and make the paint node visible
regions be their visibility within the global scene graph.

This has the side effect of plane motion causing redraws, to update
regions they've been obscuring. My assumption is that moving planes
is less frequent than damage being posted beneath an overlay, and
that we'll be more efficient for normal use cases this way.

An optimization is in place to prevent redraws when moving transparent
planes, as they haven't been occluding updates.

In addition to theoretically removing some wasteful rendering time, this
also simplifies damage accumulation.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>