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

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zmodem wrote:

> Me and Aaron are also wondering now how did it pass CI, and what's wrong with changes here. I'm sorry @zmodem that we got you involved.

Just to be clear, my comment wasn't intended as criticism of this patch. This does seem like a good opportunity to improve our presubmit testing though; filed https://github.com/llvm/llvm-project/issues/71532 .

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