A convenience subclass of QWindow that provides a Vulkan-capable
window with a double-buffered FIFO swapchain.
While advanced use cases are better served by a custom QWindow
subclass, many applications can benefit from having a convenient
helper that makes getting started easier.
Add also three examples of increasing complexity, and a variant that
shows embeddeding into widgets via QWindowContainer.
[ChangeLog][QtGui] Added QVulkanWindow, a convenience subclass of
Reviewed-by: Andy Nichols <email@example.com>