[clang] [Clang] [Tests] Refactor most unit tests to use DRAV instead (PR #115132)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman approved this pull request.

LGTM, though it may make sense to push a noop change to kickstart precommit CI into testing Windows before landing the changes.

https://github.com/llvm/llvm-project/pull/115132