[feature] Expose scope defining to other packages

If other packages could provide scope rules, it would be very helpful.

Currently, I know no way to automatically do this. I tried writing a settings file, like can be done for a grammar, but it didn't work. If it is possible this way, please let me know.

I've resorted to giving instructions in the README file on how to set it up for the specific language my autocomplete package addresses. For inexperienced users, or those completely unfamiliar with programming in general, even this can be difficult to follow.

My proposal is to add a service which expects a scope object. This way, other autocomplete packages can directly setup path completion rules, without forcing the end user to follow a set of instructions and risk ~~blowing everything up~~ getting frustrated and annoyed if it doesn't work.

I would try it myself, but I don't know anything about this package's internal logic. I only barely understood how to set up the config file myself, after a bit of trial and error.

Start by reading the package's internal logic and how its grammar settings and config file are handled. Identify where a service accepting scope objects could integrate with path-completion rules, and consider the behavior needed for another autocomplete package to configure them without README instructions.

Written by the indexing model from the issue text.