[llvm] [LV][NFC] Print VPlan's transformation pipline (PR #72665)

[Kolya Panchenko via llvm-commits]

nikolaypanchenko wrote:

> I don't think we need to add all the extra structure & complexity yet; runner macro or function taking a function_ref would suffice?

I do agree that that is good simple approach. On the other hand to do some baby step towards to pass/passmanager for vectorizer might be useful. The last commit introduces simple base class for pass, wraps all existing xforms and copies existing logic of `print-before/after*` options. If that looks to much, I'm fine to go with much simpler option

https://github.com/llvm/llvm-project/pull/72665