Fixed the issue that the MainSwitchPreference is invalid after the

page is resumed.

- MainSwithBar will be recreated after the page is resumed. We
  should keep the OnMainSwitchChangeListener for
  MainSwitchPreference and re-register the listeners after the
  page is resumed.

Bug: 225289727
Test: manual test and see the UI
Change-Id: I1b959f36fbd4c57fddf6b37ea00f11c486bbe5b9

packages/SettingsLib/MainSwitchPreference/src/com/android/settingslib/widget/MainSwitchPreference.java

@@ -144,6 +144,5 @@ public class MainSwitchPreference extends TwoStatePreference implements OnMainSw
         for (OnMainSwitchChangeListener listener : mSwitchChangeListeners) {
             mMainSwitchBar.addOnSwitchChangeListener(listener);
         }
-        mSwitchChangeListeners.clear();
     }
 }