Update icon tint color when the user toggles Dark theme

- Reload theme in slice provider when Dark theme mode changes for slices
- Reload theme in onCreate of Panel activity for its non-slice header
- Remove applyTheme from individual slices

Test: robotest
Fixes: 153700819
Change-Id: I40a7d2817c4b9100d7b2f2962a69c8a9ce6f7906

src/com/android/settings/panel/SettingsPanelActivity.java

@@ -66,6 +66,7 @@ public class SettingsPanelActivity extends FragmentActivity {
     @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
+        getApplicationContext().getTheme().rebase();
         createOrUpdatePanel(true /* shouldForceCreation */);
         getLifecycle().addObserver(new HideNonSystemOverlayMixin(this));
     }