[llvm] [VectorCombine] Add new instructions generated by deinterleave2 folding into worklist (PR #229558)

[Sam Elliott via llvm-commits]

lenary wrote:

> Perhaps we should use a custom IRBuilder inserter to add new instructions into worklist automatically, just like what InstCombine is doing right now.

Yes, this seems sensible in the longer term, to avoid more of these fix-up commits.

https://github.com/llvm/llvm-project/pull/229558