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

[David Blaikie via cfe-commits]

dwblaikie wrote:

> 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.

Repro was provided further down: https://github.com/llvm/llvm-project/pull/83124#issuecomment-2062540922

Please include test coverage and a fix before approval/recommit.

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