[llvm] [RISCV] Support vp.{gather,scatter} in RISCVGatherScatterLowering (PR #122232)

[Luke Lau via llvm-commits]

lukel97 wrote:

> FYI in our downstream vectorizer we produce vp.strided.load/store directly using stride information from SCEV. I think our plan is to do the same upstream.

I think @nikolaypanchenko mentioned this in #93972, is there an ETA? I would be +1 on doing it directly from the vectorizer, but I'm not sure how much work it would be. 

https://github.com/llvm/llvm-project/pull/122232