[clang] [Clang][Sema] placement new initializes typedef array with correct size (PR #83124)

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Sterling-Augustine wrote:

Unless the original test was subtly broken, the forward fix in 0a789ea8a829da345e46d8224d73b2ddaba6969f seems erroneous.

The forward fix changes the test to have a different declaration of `new`. But I would not expect this original change to require source-code level changes. Or was that intended?

https://github.com/llvm/llvm-project/pull/83124