[clang] [clang][Sema] Move the initializer lifetime checking code from SemaInit.cpp to a new place, NFC (PR #96758)

[Ilya Biryukov via cfe-commits]

https://github.com/ilya-biryukov approved this pull request.

LGTM, this opens up the possibility to extend this for assignments and provides better modularity!

https://github.com/llvm/llvm-project/pull/96758