[clang] Reapply "[Clang][Sema] placement new initializes typedef array with correct size (#83124)" (PR #89036)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

The original patch pointed out a regression:

https://github.com/llvm/llvm-project/pull/83124#issuecomment-2060090590

Please contact that person and get a reproducer and make sure you aren't breaking them.

https://github.com/llvm/llvm-project/pull/89036