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

[Nikita Popov via llvm-commits]

nikic wrote:

Link to the related RFC: https://discourse.llvm.org/t/a-general-purpose-loop-iteration-space-splitting-utility-loopsplitutils/91166

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