QueryDocumentSnapshot
class QueryDocumentSnapshot : DocumentSnapshotA QueryDocumentSnapshot contains data read from a document in your Firestore database as
 part of a query. The document is guaranteed to exist and its data can be extracted with the
 data property or by using subscript syntax to access a specific field.
A QueryDocumentSnapshot offers the same API surface as a DocumentSnapshot. As
 deleted documents are not returned from queries, its exists property will always be true and
 data() will never return nil.
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                  Retrieves all fields in the document as a Dictionary.Server-provided timestamps that have not yet been set to their final value will be returned as NSNull. You can use thedata(with:)method to configure this behavior.DeclarationSwift func data() -> [String : Any]Return ValueA Dictionarycontaining all fields in the document.
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                  Retrieves all fields in the document as a Dictionary.DeclarationSwift func data(with serverTimestampBehavior: ServerTimestampBehavior) -> [String : Any]ParametersserverTimestampBehaviorConfigures how server timestamps that have not yet been set to their final value are returned from the snapshot. Return ValueA Dictionarycontaining all fields in the document.