[llvm] [mlir] [mlir][arith] fix wrong floordivsi fold (#83079) (PR #83248)

[Jakub Kuderski via llvm-commits]

https://github.com/kuhar requested changes to this pull request.

@lipracer could you land the APInt change separately from the mlir fold fixes? This will make it easier to review and land properly.

https://github.com/llvm/llvm-project/pull/83248