Support for Cloud Firestore withConverter

[LucaDillenburg]

Support for Cloud Firestore type annotation and withConverter method

• Problem: The last version of the package did not work well with the new Repository<T> and Query<T> types, because the code was not type annotated. Also, it couldn't work with the withConverter method from the cloud_firestore package.
• Solution: The code was refactored to add type annotation and another class was created to both:
  1. Maintain compatibility with the last version
  2. Enable users to use the package with the withConverter method with little to no change. As explained in the README, the GeoFireCollectionWithConverterRef<T> class can be used instead of the original GeoFireCollectionRef with the only change needed to within method that now requires an extra parameter to actually get the GeoPoint from the T class.

Minor Tweaks

• Linting was added and the warnings were resolved
• Static types were prioritized instead of dynamic types
• Create withinWithDistance method that returns the DocumentSnapshot with the calculated distance (to avoid recalculations)

I would love to hear your feedbacks. :)

[awaik]

Hi! Thank you for the contribution, will review it in 1-2 days.

[awaik]

@LucaDillenburg Thank you! Package updated with your PR https://pub.dev/packages/geoflutterfire/changelog