MVKCmdClearAttachments support clearing multiple attachment layers.
MVKCmdClearImage use renderpass clear, and support clearning multiple image layers.
Rename mvkCmdClearImage() to mvkCmdClearColorImage().
MVKDevice add getFormatIsSupported() to allow devices to test for format support.
MVKFramebuffer support multiple layers.
mvk_datatypes.h support both 2D and 3D mipmap calculations and allow
mvkMTLPrimitiveTopologyClassFromVkPrimitiveTopology() in iOS.
Remove support for VK_FORMAT_B10G11R11_UFLOAT_PACK32 & VK_FORMAT_E5B9G9R9_UFLOAT_PACK32
since format components are reversed on Metal.
Move OS extension source files to new OS directory.
Update to latest SPIRV-Cross version.
Update MoltenVK version to 1.0.16.
