WIP: dozen: vulkan on d3d12

Here's a very early, very much work-in-progress version of Dozen; an implementation of Vulkan on DirectX 12.

This is able to run a couple of vulkan example applications, like vkcube. Such applications currently need modifications to run correctly, for a couple of reasons:

1. We can't yet do transitions out of VK_IMAGE_LAYOUT_UNDEFINED in render-passes.
2. We don't yet invert the vertex position written in the last vertex stage.

There's a lot more than just those two limitations, though. We also don't implement at all every driver-function needed, so applications tends to start crashing once you start resize windows, or try to shut down.

Just to repeat: This is nowhere near production-level quality at the time of writing.

This MR is put up mostly to make the community aware of our efforts, and provide visibility into what we're trying to accomplish. We expect to break out things that interfere with other drivers into smaller MRs as we move along.