[PATCH V2] RISC-V: Refactor the framework of RVV auto-vectorization

[Robin Dapp]

Hi Juzhe,

thanks, IMHO it's clearer with the changes now.  There are still
things that could be improved but it is surely an improvement over
what we currently have.  Therefore I'd vote to go ahead so we can
continue with more expanders and changes.

Still, we should be prepared for more refactoring changes in the future.

Regards
 Robin