Lightstyles remain fixed for the entire map duration. Need to implement either texture reupload in VK, or devise some other scheme of updating ligtmaps w/o texture reupload (lightstylevalues uniform buffers?).
1. Improve performance by coalescing multiple surfaces/draw calls with
the same textures (within a single brush model).
2. Add lightmaps. We don't support lightstyles yet, though, so they seem
a bit wrong at times. Also gamma handling is not great.
Oh well.
