[llvm] [LV] Move predication, early exit & region handling to VPlan0 (NFCI) (PR #185305)

[Andrei Elovikov via llvm-commits]

eas wrote:

I can see how early exits and region handling are VF-independent, but tail folding and predication aren't (at least in theory, even if they are currently). Do the latter really need to be moved?

https://github.com/llvm/llvm-project/pull/185305