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

[Ramkumar Ramachandra via llvm-commits]

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

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

```suggestion
  LLVM_ABI PHINode *getInductionVariable() const { return L->getInductionVariable(*SE); }
```

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