[llvm] [RISCV] Use vnclip for scalable vector saturating truncation. (PR #88648)

[Luke Lau via llvm-commits]

lukel97 wrote:

> Pending on #88496

I think it should be fine to merge this before #88496? It should be easy enough to update the patterns added in this PR later

https://github.com/llvm/llvm-project/pull/88648