Move MVKVulkanAPIObject to its own .h/mm files. Add MVKCmdDebug.h/mm files. Change extension on MVKExtensions.cpp and MVKBaseObject.cpp to .mm. Remove unused command use in MVKQueue submit() and waitIdle() functions. MVKCommandPool constructor use default isPooling value in MVKCommandTypePool constructors. MVKSwapchainImage pass image index in constructor.