Add support for the `dzn` Vulkan driver

As reported in archlinux/archlinux-wsl#8 (closed), WSL2 recently introduced support for Vulkan through the d3d12 Gallium and dzn (also known as microsoft-experimental) Vulkan drivers.

I'm opening this issue to discuss the possibility to add support for that dzn Vulkan driver in our mesa package. As of now, people are relying on an AUR package for it but, since we now provide an official WSL image, maybe it make sense to support it in our official mesa package now? 🤗