The CPU copy is horribly slow, so let's hook-up DXGI swapchains. Note that we're still limited in term of features. For instance, we can't support more than 2 images per swapchain because of the DXGI present ordering constraint. We also have to do an extra copy when the image is to be used as a storage image because D3D12 doesn't allow it.
Marked as draft because I'm not entirely happy with the
and I also don't know if @jekstrand will agree with the new naming in
vulkan/wsi: Add support for image -> image blits or the idea of adding
image -> image blits to the core.