[clang] [clang-tools-extra] [clang][NFC] Refactor `CXXNewExpr::InitializationStyle` (PR #71322)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

> If you see failures locally, it's best to understand where they coming from: even if it passes on bots it just means we have a hole in our test coverage.

Sure, but it wasn't the first time I've seen local test failures that doesn't reproduce anywhere else (`Clang :: LibClang/symbols.test`). By the time I merged this PR, me and Aaron have spent hours staring at the changes without any progress. So we wanted an additional confirmation that this is not in the same as `Clang :: LibClang/symbols.test` failure, especially looking at pre-commit CI that reported just a several seemingly unrelated clang-tidy failures. I hope it is acceptable that we decided not to spend even more time before trying this PR out on wider range of buildbots.

https://github.com/llvm/llvm-project/pull/71322