Some volumes have very obvious staircase artifacts:  As suggested by @SnowWindSaveYou [we could use cubic sampling to solve this](https://github.com/mlavik1/UnityVolumeRendering/issues/112#issuecomment-1276964625). Since this can be expensive, we should create a setting for cubic sampling.