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

[Jakub Kuderski via llvm-commits]

https://github.com/kuhar commented:

The PR subject line doesn't match the function names anymore. Could you update it?

Thanks for all the fixes so far. In general looks good, my only remaining comments are related to the documentation.

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