🔒️ Restrict the geofence location event to the current package

This is one of the security recommendations
https://developer.android.com/develop/background-work/background-tasks/broadcasts#java

I also tried to change the receiver to be NOT_EXPORTED, but could not get that
to work in the limited time available.

I also tried to send the message via an Intent that specified the context and
the class, but that does not work with broadcast intents
e-mission/e-mission-docs#1079 (comment)

Testing done:
- Before the change

```
08-27 22:36:18.466  4901  5581 I GeofenceLocationIntentService: broadcasting intent Intent { act=GEOFENCE_LOCATION_RESULT (has extras) }
```

- After the change

```
08-27 22:42:29.312  6785  7442 I GeofenceLocationIntentService: broadcasting intent Intent { act=GEOFENCE_LOCATION_RESULT pkg=edu.berkeley.eecs.emission (has extras) }
```

src/android/location/actions/GeofenceLocationIntentService.java

@@ -112,6 +112,7 @@ protected void onHandleIntent(Intent intent) {
 
     private void broadcastLoc(Location loc) {
         Intent answerIntent = new Intent(INTENT_NAME);
+        answerIntent.setPackage(this.getPackageName());
         answerIntent.putExtra(INTENT_RESULT_KEY, loc);
         Log.i(this, TAG, "broadcasting intent "+answerIntent);
         LocalBroadcastManager.getInstance(this).sendBroadcast(answerIntent);