GL-compatible godrays

[HumanoidSandvichDispenser]

The godrays render differently between the Forward+ (Vulkan) renderer and the Compatibility (OpenGL) renderer. The godrays shader should be rewritten to be compatible with both of them.

[HumanoidSandvichDispenser]

The problem is that the Vulkan and OpenGL renderers render shaders differently if the texture is a blank CanvasTexture. Adding an existing texture (with size greater than 1x1) will make OpenGL render shaders closer to Vulkan as the texture size increases.