[llvm] [DomTreeUpdater] Move critical edge splitting code to updater (PR #115111)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

Could you click the `Resolve conversation` button on comments that have been addressed? Overall, the patch seems OK to me, but this requires someone to review the logic. I, unfortunately, don't have the time to do this. Would you be able to find a secondary reviewer?

https://github.com/llvm/llvm-project/pull/115111