[llvm] [APInt] Restore multiplicativeInverse with explicit modulus and better testing (PR #87812)

[Jeremy Kun via llvm-commits]

j2kun wrote:

Adding review comments to a "revert" PR sends mixed messages :)

I'm happy to sit on this PR until there's an in-tree user, which I intend to add. In the mean time you can let me know if the testing is exhaustive enough for LLVM standards. I did not change the implementation.

https://github.com/llvm/llvm-project/pull/87812