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

[Ramkumar Ramachandra via llvm-commits]

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artagnon wrote:

```suggestion
  LLVM_ABI unsigned getNumPartitions() const { return Partitions.size(); }
```

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