[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/p2p/WifiP2pSettings.java

@@ -200,7 +200,7 @@ public class WifiP2pSettings extends DashboardFragment
     public void onActivityCreated(Bundle savedInstanceState) {
         final Activity activity = getActivity();
         if (mWifiP2pManager == null) {
-            mWifiP2pManager = (WifiP2pManager) getSystemService(Context.WIFI_P2P_SERVICE);
+            mWifiP2pManager = getSystemService(WifiP2pManager.class);
         }
 
         if (mWifiP2pManager != null) {