Enable GLon12 on Windows CI

[cwfitzgerald]

With #4248 on the horizon, we want to be able to test it, which requires GL setup on windows on the headless machines. We can use GLon12

Here is the dialog I had with Jesse on the DX12 discord about how to set this up. We should look at the mesa build option.

cwfitzgerald: Before I go down this rabbit hole of possibly setting this up - is it possible to use GLon12 on top of warp to get a gl device when you don't have a gpu (trying to test gl on windows in CI)
Jessie: Yes
Jessie: That's how we test GLOn12 in Mesa CI
cwfitzgerald: Oh nice! Is there any docs on how to actually set up GLon12?
Jessie: The easiest way is just install the GL/CL compat pack from the Microsoft store. On a server SKU for CI though that might be tricky. There is a version available that should be installable on server from https://github.com/microsoft/OpenCLOn12/releases/tag/v1.2112.2.0 but that's a bit stale - I need to put up a new one at some point
Jessie: The other option is to build it or grab a Mesa build from https://github.com/pal1000/mesa-dist-win/releases and drop the opengl32.dll and other DLLs from that package next to the .exe you're looking to test to override the OS's OpenGL ICD loader
cwfitzgerald: This solution looks likely the easiest to pull off in CI at least - with the gl/cl compat package, if there a way to force its use for local testing purposes?
Jessie: It kicks in if there's no GL driver. You can do that by disabling your GPU (including the GL driver), or by modifying the registry to unregister the GL driver
cwfitzgerald: Alright, it sounds like it would be easier to do the Mesa dll thing locally as well anyway
cwfitzgerald: Thanks for all the info! 
Jessie: Happy to have more people using this stuff