Add fog occlusion for biome fog

[ikabod-kee]

[IntegratedQuantum]

So it wouldn't draw stuff behind the fog?

[ikabod-kee]

Correct!

[IntegratedQuantum]

I don't think this is feasable. A simple heuristic (like assuming the biome fog density as the highest density) won't work because placed blocks can have less dense fog. So we only know the fog density of pixel after transparent rendering, and since that's the last stage we cannot cull anything based on that.