Add support for more VkResolveModeFlagBits

[billhollings]

For native MSAA on the GPU, Metal uses the equivalent of AVERAGE. For simplicity, MoltenVK uses SAMPLE_ZERO in the compute kernel when native MSAA is not supported.

As an enhancement, we could add support to the kernel function to resolve the other resolve modes. We could also run the compute kernel anytime a resolution mode other than AVERAGE is requested.