dzn: Add a DXCore enumeration path

dzn: Add a DXCore enumeration path

WSL doesn't have DXGI, but it does have DXCore. DXCore also has a nice
property that it filters to only D3D12-capable adapters. We can rely
on DXCore as a first option even for Windows, because we'll be able
to let the Vulkan loader do preference sorting, instead of having to
rely on DXGI to do it for us.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Bill Kristiansen <billkris@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17340>