Port Refactorex into Expert

Refactorex is an excellent project that we depend on for several code actions.

However its original use case was different and integrating it with expert has some compatibility issues, mainly around dealing with offset conversions, or odd corner cases we've found from expert users.

I think it's worth to port its features(with proper attribution) into expert itself for two reasons:

• To eliminate the compatibility glue and apply expert-specific optimizations where needed
• To allow us to fix issues quickly, and not put the entire burden on the one maintainer of Refactorex

cc @gp-pereira as the Refactorex author