[llvm] [VPlan] Add transformation to narrow interleave groups. (PR #106441)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

I landed the load->store group only transform separately as c73ad7ba204fa05b074c1316b2244063aa10410f as suggested.

Will land the changes in the PR soon as well

https://github.com/llvm/llvm-project/pull/106441