[llvm] [Passes] Move LoopInterchange into optimization pipeline (PR #145503)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Makes sense in general but do you have any data on how this change impacts the # of loops interchanged, and the impact on perf for the cases where it helps?

This should also at least have a test checking the position of LoopInterchange in the pipline and ideally a phase-ordering tests that shows an improvement

https://github.com/llvm/llvm-project/pull/145503