[llvm] [workflows] Port buildkite Windows config to GitHub actions (PR #82093)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

Shall we actually setup a proof of concept custom GCP Windows runner? Then we can just invite Google to actually migrate the buildkite runners to GitHub instead. I seem to recall Microsoft ready to provide some machine as well? (@AaronBallman  knows maybe?).
Having more beefy machines (+ having sizable local persistent sccache as well). may just be what we need here.

https://github.com/llvm/llvm-project/pull/82093