[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/TetherService.java

@@ -255,7 +255,7 @@ public class TetherService extends Service {
     }
 
     private void disableTethering(final int tetheringType) {
-        final TetheringManager tm = (TetheringManager) getSystemService(Context.TETHERING_SERVICE);
+        final TetheringManager tm = getSystemService(TetheringManager.class);
         tm.stopTethering(tetheringType);
     }