[SLP]Support freeze as copyable main op
Model non-freeze lanes as freeze(V), which refines V, so mixed
bundles become a single vector freeze instead of a gather.
Assisted-by: Cursor
Original Pull Request: https://github.com/llvm/llvm-project/pull/239999
Reviewers:
Pull Request: https://github.com/llvm/llvm-project/pull/241009
