[llvm] [VPlan] Introduce VPlanConstantFolder (PR #125365)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

@nikic I'm not sure how the ConstantExpr creation ties into your effort to remove constant-expressions. Could you kindly have a look?

https://github.com/llvm/llvm-project/pull/125365