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

[Erich Keane via cfe-commits]

erichkeane wrote:

> @mahtohappy can we please revert this in the meantime while you look for a fix here. Feel free to land it again with the fix.

He's likely outside of work hours, but feel free to submit a revert.

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