tests/vkd3d-shader-api: Refactorings to allow dxcompiler and Vulkan use in the shader API tests.
Storage buffer UAVs are currently not tested, and vkd3d does not use them. Testing can be accomplished using the BUFFER_UAV flag in the API tests, but we need to make dxcompiler and Vulkan helpers available there first.
Edited by Conor McCarthy