The system now uses several 3D textures in order to decouple every steps of the volumetric rendering.
See https://www.ea.com/frostbite/news/physically-based-unified-volumetric-rendering-in-frostbite for more details.
On the technical side, instead of using a compute shader to populate the 3D textures we use layered rendering with a geometry shader to render 1 fullscreen triangle per 3D texture slice.
rna_scene.c was getting way too big with data that was related to
DNA_layer_types.h.
I tried doing it earlier, but failed. But now with the new changes I think it's
better to do this sooner than later.
