[Settings] Enable access from non-UI thread

To support query from settings intelligent, these listeners need to
support accessing from non-UI thread.

Bug: 149543756
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=ActiveSubsciptionsListenerTest
Change-Id: I768f41f76d0223634be2b728d33fa0cfcc69fe69

src/com/android/settings/network/ProxySubscriptionManager.java

@@ -72,7 +72,7 @@ public class ProxySubscriptionManager implements LifecycleObserver {
     private static ProxySubscriptionManager sSingleton;
 
     private ProxySubscriptionManager(Context context) {
-        final Looper looper = Looper.getMainLooper();
+        final Looper looper = context.getMainLooper();
 
         mActiveSubscriptionsListeners =
                 new ArrayList<OnActiveSubscriptionChangedListener>();