[llvm] [Transforms][Utils] Add LoopSplitUtils for iteration-space loop splitting (PR #205995)

[Ramkumar Ramachandra via llvm-commits]

================

----------------
artagnon wrote:

```suggestion
    BranchInst::create(S.FinalExit, Exiti);
    BranchInst::create(S.FinalExit, Guardi);
```

to avoid creating a temporary Builder unnecessarily?

https://github.com/llvm/llvm-project/pull/205995