Remove more callback doc references & some small other changes

[hasezoey]

Summary

This PR does a bunch of small maintenance things, mainly removing more callback documentation references, some other changes include:

• remove Double from being assigned in index.js because it does not exist in mongoose
• import & export MongooseError once
• use consistent error constructors for mongoose::model
• assign more function names (to not have them be anonymous anymore)
• remove "always true" path in model::aggregate
• expose Connection::on and Connection::once to the documentation
• update @typescript-eslint/* to fix warning in npm lint

[vkarpov15]

Thanks 👍