[clang] [clang][NFC] Refactor expected directives in C++ DRs 1-99 (PR #73879)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

I'm putting this NFC for a review, because that's the direction I'd like our DR test suite to take. If it goes well, I'll go on and refactor the rest of the test suite in this manner.

https://github.com/llvm/llvm-project/pull/73879