[llvm] [VPlan] Pre-commit test for VPWidenCanonicalIVRecipe cost (NFC) (PR #195014)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon commented:

> I need to use stacked PR for this

Just note that it's acceptable to create just one PR, with the first commit being the pre-commit test, and the top commit with the code change, showing the diff to the test -- I think we actually prefer it this way?

https://github.com/llvm/llvm-project/pull/195014