TODO [GFX]: Move composite passes (volumetric clouds and blur) from pixel to compute

[steaklive]

It probably makes sense to move everything to compute to keep the end of the frame compute-only (I can't remember any other pixel passes along the way) without flushing/switching to graphics work. We might gain some performance.

The best way would be to keep both pixel and compute versions and choose one based on the hardware, however, that might be tedious to support in such project.