[llvm] [VPlan] Simplify vp.merge true, (or x, y), x -> vp.merge y, true, x (PR #135017)

[Luke Lau via llvm-commits]

lukel97 wrote:

> I think we could also have non-widened intrinsic calls in VPReplicateRecipe. I guess also matching those and having a generic m_Intrinsic would add a substantial amount of extra logic?

We can do it if we copy the m_Intrinsic stuff from PatternMatch.h, I've gone ahead and done it in 5737af159552a6e4a37fdb9cdf4e490678f52836

There's a whole bunch of templates needed so if it's too much I'm happy to go with the previous approach either. Although I think this new approach is a bit cleaner as hijacking the opcode field of `Recipe_match` wasn't great

https://github.com/llvm/llvm-project/pull/135017