[llvm] [VPlan] Add incoming_[blocks,values] iterators to VPPhiAccessors (NFC) (PR #138472)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Does the PR title need updated? VPPhiAccessors was already added in #129388, this is adding more methods to it right?

Yep, updated, thanks

https://github.com/llvm/llvm-project/pull/138472