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

[Shafik Yaghmour via cfe-commits]

shafik wrote:

Thank you for this fix.

Can you put more details in your summary. The approach I like to take is 1. what the problem is 2. what is the approach of the fix 3. any other important details.

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