appendMessage method
添加多Element消息。待废弃
注意 4.0.3 以及之后版本支持,web 版本不支持
Implementation
Future<V2TimValueCallback<V2TimMessage>> appendMessage({
  required String createMessageBaseId,
  required String createMessageAppendId,
}) async {
  if (kIsWeb) {
    return TencentCloudChatSdkPlatform.instance.appendMessage(
      createMessageAppendId: createMessageAppendId,
      createMessageBaseId: createMessageBaseId,
    );
  }
  V2TimMessage message = TIMMessageManager.instance.appendMessage(
    createMessageAppendId: createMessageAppendId,
    createMessageBaseId: createMessageBaseId,
  );
  return V2TimValueCallback<V2TimMessage>.fromObject(message);
}