[Settings] Support getSystemService(Class<T>)

Add getSystemService(Class<T>) to align the capability with framework
part.

This is a back port from aosp/1639943, aosp/1645152 and aosp/1648047

Bug: 179640862
Test: local
Change-Id: I035db55a71f94000ca35f8d71f03c19208423c73

src/com/android/settings/wifi/tether/WifiTetherSettings.java

@@ -110,7 +110,7 @@ public class WifiTetherSettings extends RestrictedDashboardFragment
     @Override
     public void onAttach(Context context) {
         super.onAttach(context);
-        mWifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
+        mWifiManager = context.getSystemService(WifiManager.class);
         mTetherChangeReceiver = new TetherChangeReceiver();
 
         mSSIDPreferenceController = use(WifiTetherSSIDPreferenceController.class);