Figure out how to use Float textures on iOS

[gkjohnson]

Currently half float textures are used on ios and any platform that doesn't support float texture blending. However this will result in heavily skewed colors during blending. Screenshots after ~ 5000 samples

HalfFloat

Float

[gkjohnson]

On ios we can render to two buffers and manually blend while using nearest filter instead of relying on hardware support. Or we can perform the blend in the raytracing buffer itself.