Implement Query.where with whereIn about fake_cloud_firestore

[atn832]

This is where it should be implemented: https://github.com/atn832/cloud_firestore_mocks/blob/65a0655f0ade657957d2e00e3154775e466103df/lib/src/mock_query.dart#L89

[diegoveloper]

hi @atn832 beside from that class, in which class should we add the tests?

[atn832]

@diegoveloper in here: https://github.com/atn832/cloud_firestore_mocks/blob/master/test/mock_query_test.dart

And also (optionally) in https://github.com/atn832/cloud_firestore_mocks/blob/master/test_driver/cloud_firestore_behaviors.dart. This is to test that our custom implementation behaves the same as the real Firebase and the Firebase emulator.

[anu-rock]

I need this functionality in one of my apps. Opened a PR that hopefully fixes this.