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

[Jakub Kuderski via llvm-commits]

kuhar wrote:

@Sh0g0-1758 I don't have the wider context but this PR looks like a nice code cleanup on its own.

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