@shedaniel noted that world and blockpos parameters are missing from FluidVariantRenderHandler, whereas a @Nullable NbtCompound parameter is missing from FluidRenderHandler. And we can get rid of the FluidState parameter as it can be queried from the world if needed with close to 0 overhead.

So we should combine both, probably by expanding FluidRenderHandler. We can then remove FluidVariantRenderHandler in a further iteration of the transfer API.

Additionally, the API should add a 1 << 24 mask for the alpha, or at least mention in the javadoc. Something like that...