Forces that could run along with cops

[marcandre]

We are starting to have cops using the Regexp parser (like #8407).

I'd like to factorize that parsing.

It could be done in a shared module, maybe with a global registry of regexp to avoid parsing the same regexp many times, but I was thinking that another way would be a ParsedRegexp force that would do the parsing and call on_parsed_regexp for those cops that want to use it (2 right now). This would require that Forces to be allowed to respond to the same callbacks than cops at the same time though (so that on_parsed_regexp from the force and on_nth_ref from Commissionner are fired in the right alternance).

We have currently only a single Force in the builtin gem (VariableForce). It does it's own processing and wouldn't be affected as it uses process_rescue and not on_rescue. Other forces might. Are there other known examples? Is it worth keeping compatibility by defining a different Force::Base?

[marcandre]

Closing in favor of #8510