[llvm] [ADT] Add signed and unsigned mulHi and mulLo to APInt (PR #84719)

[Jakub Kuderski via llvm-commits]

https://github.com/kuhar requested changes to this pull request.

Could you also address things I raised on the other PR for mulh?
https://github.com/llvm/llvm-project/pull/84609#pullrequestreview-1926301585 and the other comments that follow

https://github.com/llvm/llvm-project/pull/84719