[llvm] [mlir] [ADT] Add implementations for mulhs and mulhu to APInt (PR #84609)

[Shourya Goel via llvm-commits]

Sh0g0-1758 wrote:

@kuhar, I have implemented the MLIR changes and the tests are passing. For the signed comments, I tried to keep it concise, I wrote a kinda draft for the comments but it was taking up a lot of space, so decided to keep it short. 

https://github.com/llvm/llvm-project/pull/84609