This file changes the non-dispatchable Vulkan handle types. We want to
use some of these handles in utils/VulkanSwapChain.cpp so it needs to
have access to it. The file could include
backend/vulkan/vulkan_platform.h but it seems a bit cleaner to move the
header in common/ instead with a warning if the Vulkan backend isn't
enabled.
This as this is the first command handled by the Vulkan backend, this
commit also introduces the b:✌️:CommandBUffer class and implements
b:✌️:Queue::Submit.
Also enables the BufferSetSubData tests that are now passing on Vulkan
even though the buffer transitions are unimplemented.