[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/vpn2/AppManagementFragment.java

@@ -319,7 +319,7 @@ public class AppManagementFragment extends SettingsPreferenceFragment
     @VisibleForTesting
     static boolean appHasVpnPermission(Context context, @NonNull ApplicationInfo application) {
         final AppOpsManager service =
-                (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
+                context.getSystemService(AppOpsManager.class);
         final List<AppOpsManager.PackageOps> ops = service.getOpsForPackage(application.uid,
                 application.packageName, new int[]{OP_ACTIVATE_VPN, OP_ACTIVATE_PLATFORM_VPN});
         return !ArrayUtils.isEmpty(ops);