[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/WifiConfigInfo.java

@@ -38,7 +38,7 @@ public class WifiConfigInfo extends Activity {
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
 
-        mWifiManager = (WifiManager) getSystemService(WIFI_SERVICE);
+        mWifiManager = getSystemService(WifiManager.class);
         setContentView(R.layout.wifi_config_info);
         mConfigList = (TextView) findViewById(R.id.config_list);
     }