Add MVKShaderStageResourceBinding::resourceIndex to accumulate unique index across
all resource types, and refactor calculation of indices to accommodate this value.
Create SVOT in descriptors for Metal arg buffer indices.
Remove MVKDescriptorSetLayoutBinding::_metalArgumentBufferIndex
and use MVKShaderStageResourceBinding::resourceIndex instead.
Refactor calculation of MVKDescriptorSetLayout::_metalArgumentBufferSize.