[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

tests/robotests/src/com/android/settings/wifi/WifiEnablerTest.java

@@ -53,7 +53,7 @@ public class WifiEnablerTest {
     @Before
     public void setUp() {
         MockitoAnnotations.initMocks(this);
-        when(mContext.getSystemService(Context.WIFI_SERVICE)).thenReturn(mWifiManager);
+        when(mContext.getSystemService(WifiManager.class)).thenReturn(mWifiManager);
         mEnabler = new WifiEnabler(mContext, mock(SwitchWidgetController.class),
                 mock(MetricsFeatureProvider.class), mConnectivityManager);
     }