[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:

Where is the repro from the original author?  What did they share, and what ended up being the solution/test here for it?

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