[llvm] [ConstantFolding] Add folding for [de]interleave2, insert and extract (PR #141301)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

These make sense to have, but I'm wondering if you were seeing any cases where we were using fixed length versions of these intrinsics. From my understanding these are only really used for scalable vectors in the loop vectorizer etc.

Maybe from the ComplexDeinterleaving pass?

https://github.com/llvm/llvm-project/pull/141301