[llvm] [VPlan] Use DomTreeUpdater to automatically update DT for vector loop. (PR #92525)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Worth separating into two NFC's: one simplifying how legacy updates its DT, and another which teaches native to start update its DT?

Updated to only pass DT to DTU in non-native path, which makes DTU updates a no-op in that case

https://github.com/llvm/llvm-project/pull/92525