[llvm] [RISCV] Re-work how VWADD_W_VL and similar _W_VL nodes are handled in combineOp_VLToVWOp_VL. (PR #159205)

[Pengcheng Wang via llvm-commits]

https://github.com/wangpc-pp approved this pull request.

LGTM.

I think this needs to be backported to llvm 21?

https://github.com/llvm/llvm-project/pull/159205