Add DocumentSnapshot.entries to Firestore

[brettwillis]

With the current API, there is no way to retrieve unknown fields from a DocumentSnapshot, only known fields can be retrieved (e.g. with contains() and get()).

The DocumentSnapshot needs to also expose a map-like API, like below:

val size: Int
val entries: Set<Pair<String, Any>>
val keys: Set<String>
val values: Collection<Any>

This allows enumeration of all fields, not just those known at compile-time.

[nbransby]

Thanks @brettwillis could you attach links to the relevant class members from the native firebase sdk reference documentation?

[brettwillis]

getData() returns a Map<String, Any>, which allows enumeration of arbitrary keys and values.

You could either implement a Map-like interface directly on the DocumentSnapshot class, or implement getMap() or something which returns the native Map<String, Any>...