Add package filtering to NLSes

Now users can prevent a given notification listener from seeing
notifications from particular apps.

Test: settings unit tests
Bug: 173052211
Change-Id: Ia868d6dc2da1ae7f75c0dca47034e28910584acd

src/com/android/settings/notification/NotificationBackend.java

@@ -49,6 +49,7 @@ import android.service.notification.NotificationListenerFilter;
 import android.text.format.DateUtils;
 import android.util.IconDrawableFactory;
 import android.util.Log;
+import android.util.Slog;
 
 import androidx.annotation.VisibleForTesting;