[llvm] [VPlan] Add initial VPScalarEvolution, use to get trip count SCEV (NFC) (PR #94464)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Thanks, comments should addressed! 

@rengolin WDYT about the latest version?

https://github.com/llvm/llvm-project/pull/94464