Currently the generated of Fragment functions use same sampler for all textures in a fragment function.
But there are several fragment functions that use more than one texture and the sampler can be different for each texture.
We should support setting separate samplers for each texture.
There are two possible approaches.
1. Set MTLSamplerState for each texture through the uniform struct.
OR
2. Pass the MTLSamplerState as attributed fragment function argument.