[llvm] [RISCV][VLOPT] Add support for Vector Fixed-Point Arithmetic Instructions (PR #126483)

[Michael Maitland via llvm-commits]

https://github.com/michaelmaitland approved this pull request.

Nice! I had previously skipped over these because of vxsat, but its a great idea to check if vxsat is dead!

LGTM

https://github.com/llvm/llvm-project/pull/126483