[llvm] [RISCV][ISel] Combine vector fadd/fsub/fmul with fp extend. (PR #81248)

[Wang Pengcheng via llvm-commits]

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

LGTM. Please wait some time to see if there are more comments.

https://github.com/llvm/llvm-project/pull/81248