Align the "Open activity" UI style with usual accessibility service "Use service"

Root Cause: "Open activity" Preference is not part of the widget SettingsMainSwitchBarPreference, so its UI style did not be inherited.

Solution: "Open activity" has different concept from switch bar, we need to manual set its bacground to comply with the SettingsLib style.

Bug: 207067203
Test: manual test
Change-Id: I66f63f6952e5c4770509febc0e53eca6dc6eedb9

src/com/android/settings/accessibility/LaunchAccessibilityActivityPreferenceFragment.java

@@ -150,6 +150,7 @@ public class LaunchAccessibilityActivityPreferenceFragment extends ToggleFeature
 
     private void initLaunchPreference() {
         final Preference launchPreference = new Preference(getPrefContext());
+        launchPreference.setLayoutResource(R.layout.accessibility_launch_activity_preference);
         launchPreference.setKey(KEY_LAUNCH_PREFERENCE);
 
         final AccessibilityShortcutInfo info = getAccessibilityShortcutInfo();