fix(messaging, android): avoid using rn61+ symbol

this should be the inline equivalent of the rn61 symbol I added
in #5236 - accidentally breaking react-native 0.60 compatibility

Author: mikehardy

packages/messaging/android/src/main/java/io/invertase/firebase/messaging/ReactNativeFirebaseMessagingModule.java

@@ -29,6 +29,7 @@
 import com.facebook.react.bridge.ReactMethod;
 import com.facebook.react.bridge.ReadableMap;
 import com.facebook.react.bridge.WritableMap;
+import com.facebook.react.bridge.WritableNativeMap;
 import com.google.android.gms.tasks.Tasks;
 import com.google.firebase.iid.FirebaseInstanceId;
 import com.google.firebase.messaging.FirebaseMessaging;
@@ -231,7 +232,9 @@ public void onNewIntent(Intent intent) {
 
         if (remoteMessageMap != null) {
           // WritableNativeMap not be consumed twice. But it is resolved in future and in event below. Make a copy - issue #5231
-          initialNotification = remoteMessageMap.copy();
+          WritableNativeMap newInitialNotification = new WritableNativeMap();
+          newInitialNotification.merge(remoteMessageMap);
+          initialNotification = newInitialNotification;
           ReactNativeFirebaseMessagingReceiver.notifications.remove(messageId);
 
           ReactNativeFirebaseEventEmitter emitter = ReactNativeFirebaseEventEmitter.getSharedInstance();