Add renderOverlay render stage
So we can render gui and overlays after transmission. That would be additional stage on top of existing renderBackground, renderOpaque, renderTransparent.
Should the overlay renderer be brought back to core too then? (currently ported in examples)
https://github.com/pex-gl/pex-renderer/blob/7d41f4a67e873729fc4bc854d50518004ffc1e58/examples/camera-cinematic-dof.js#L96-L140
Yes but it would have to support al the features latest gl.TextureOverlay from Dent... project has: percentage vs pixel size, keeping texture aspect ratio + cover mode (should be implemented as fit/cover), checked with proper gamma correction, support for transparency but also turning off transparency etc.