[llvm] [IR] Add new CreateVectorInterleave interface and constant fold (PR #150931)

[David Sherwood via llvm-commits]

david-arm wrote:

I had to add `FoldVectorInterleave` to all of the folders, but I think only one of the folders is being exercised. I wasn't sure if it was worth adding explicit tests for instsimplify and for the target folder.

https://github.com/llvm/llvm-project/pull/150931