[llvm] [RISCV] Generalize (sub zext, zext) -> (sext (sub zext, zext)) to add (PR #86248)

[Philip Reames via llvm-commits]

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

LGTM as well.

Minor, but what is the "ve" abbreviation you use everywhere?  You should probably spell that out.  

https://github.com/llvm/llvm-project/pull/86248