[llvm] [TypeMetadataUtil][CallPromtionUtil]Add utility function getFunctionAtVTableOffset that finds functions through alias. Use it in CallPromotionUtils which didn't promote aliasee previously (PR #80736)

[Teresa Johnson via llvm-commits]

https://github.com/teresajohnson commented:

Suggest making the PR title shorter and moving some of the details there currently to the description. Also, I think this can be marked NFC?

https://github.com/llvm/llvm-project/pull/80736