Add a feature flag for the special access to the long background task

The entry should be hidden if the RUN_LONG_JOBS can't be toggled.

Bug: 255821578
Test: atest AppFilterRegistryTest
Test: make -j RunSettingsRoboTests \
ROBOTTEST_FILTER="LongBackgroundTasksDetailsTest|
LongBackgroundTasksDetailsPreferenceControllerTest"
Test: Manually check the Settings page

Change-Id: Ib1c58d93b40afefdf3ca666c661e213d01c542c6

src/com/android/settings/applications/ApplicationFeatureProvider.java

@@ -92,6 +92,12 @@ public interface ApplicationFeatureProvider {
         return "";
     }
 
+    /**
+     * @return {@code true} if the device supports the toggling of the long background task
+     * permission.
+     */
+    boolean isLongBackgroundTaskPermissionToggleSupported();
+
     /**
      * Callback that receives the number of packages installed on the device.
      */