[llvm] [VPlan] Perform optimizeMaskToEVL in terms of pattern matching (PR #155394)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Is this patch NFC?

Not really because we no longer convert recipes without a header mask, which might be fixing a correctness issue. As you mention though I'm not sure if we get any edge cases that hit this today. Hopefully not!

https://github.com/llvm/llvm-project/pull/155394