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

[Quentin Colombet via llvm-commits]

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

Nice refactor / extension!

I only had a cursory look so maybe wait on someone with a higher stake than me in the RISC-V backend.

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