[clang] [clang-tools-extra] [clang][NFC] Refactor `CXXNewExpr::InitializationStyle` (re-land) (PR #71417)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> > The enum we had in the past described the syntax of the new expression.
> 
> Even if it was the case at some point, I'm not sure it held when I created the PR, which eliminated this kind of nasty mapping, encoding how this enum was actually used:
> 
> ```c++
>  CXXNewExprBits.StoredInitializationStyle =
>       Initializer ? InitializationStyle + 1 : 0;
> ```
> 
> ```c++
>   InitializationStyle getInitializationStyle() const {
>     if (CXXNewExprBits.StoredInitializationStyle == 0)
>       return NoInit;
>     return static_cast<InitializationStyle>(
>         CXXNewExprBits.StoredInitializationStyle - 1);
> ```

Yeah, perhaps calling this NFC was a stretch because it does have a minor functional change in what it expresses; sorry for that confusion! I think the current form is a more clean way to express the code. Are you finding it's causing issues beyond just the change to test behavior?

https://github.com/llvm/llvm-project/pull/71417