[llvm] Reland: [LV]: Teach LV to recursively (de)interleave. (PR #122989)

[Florian Hahn via llvm-commits]

fhahn wrote:

It sounds like `getInterleaveGroupCost` and `VPInterleaveRecipe::computeCost` don't agree on costs with scalable VFs if the factor is > 2.  I assume this wasn't a problem before as this case couldn't happen, but is exposed by this patch.

https://github.com/llvm/llvm-project/pull/122989