[clang] [clang] Migrate DR tests to `static_assert` (PR #88611)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> (especially considering you said you’re going to refactor more tests than just these)

@Sirraide I didn't say that originally, but you reminded me that I indeed forgot about all the uses of arrays that don't trigger diagnostics. I went over all of them, and decided to include them in this patch instead of doing a follow-up NFC commit, since it's not too much of them actually.

https://github.com/llvm/llvm-project/pull/88611