[llvm] [Transforms][Utils] Add LoopSplit for iteration-space loop splitting (PR #217232)

[Caroline Newcombe via llvm-commits]

https://github.com/cenewcombe commented:

I have left a few inline comments after further review. I am fairly new to this part of LLVM, so feel free to let me know if I've missed something on any of these points. Thanks for working on this!

https://github.com/llvm/llvm-project/pull/217232