d3d12: GL4.6

This enables a bunch of trivial extensions that were all already implemented, as well as flipping on the switch for SPIR-V (lightly tested locally, CI is busted), fixing the QBO shaders for pipeline stats, and hooking up SO overflow queries, which turned out to be a lot of work. And it wouldn't be a new feature without exposing yet another bug in WARP...

The SPIR-V tests are all broken in CI, due to missing piglit support and broken spirv-as.exe in the Vulkan runtime. Fixes to these components have been merged upstream to their respective repos, CI changes to consume those updates here will be tackled separately.