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

[Shourya Goel via llvm-commits]

Sh0g0-1758 wrote:

@jayfoad, made the changes. I was under the impression that something similar to `DivisionByConstantTest.cpp` needed to be changed, so that did not catch my attention. 

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