⚠️ BREAKING: Based the parsers/serializers on Base instead of IReadOnlyDictionary<>. Should not really matter, since internally, the code required the things to be subclasses of Base anyway to function correctly.
Added extensions so subtrees van be serialized, if the underlying engine is our new POCO serializer
Added extensions so one can serialize to/from streams, if the underlying engine is our new POCO serializer.
⚠️ BREAKING: Removed the obsolete FhirJsonConverter constructors (use the ForFhir extension methods on JsonSerializerOptions).
⚠️ BREAKING: Renamed methods on the IFhirSerializationExtensions, since they made no sense (e.g. DeserializeReaderToJson has become DeserializeFromJsonReader).
DeserializeReaderToJsonhas becomeDeserializeFromJsonReader).Fixes #2917.