We're having trouble using `texture3d<half, access::read>` on iPhone X.
Our tests pass on older iPhones, and all iPads.
When we change to texture3d<float, access::read> on iPhone X, our tests pass (without needing to change the underlying texture from `R16Float` to `R32Float`, interestingly).
Is anyone else having trouble with texture3d on iPhone X? I'm guessing texture3d<half, ...> is a fairly rare use-case.
