Ensure hibernation exemption toggle uses pre-S flag

For dogfood, we want hibernation to target apps that target pre-S. This
was done on the PermissionController side but the toggle in Settings
did not visually reflect this policy, confusing dogfood/teamfood
participants.

This updates the default toggle position to consider whether the pre-S
flag is on and then default to the "on" position for apps targeting
pre-S if the flag was on for the device.

Bug: 189260947
Test: atest HibernationSwitchPreferenceControllerTest
Test: manual
Change-Id: I9cd16e82e1eee4589cb17a356b6bf2e3297a8dd2

src/com/android/settings/Utils.java

@@ -161,6 +161,10 @@ public final class Utils extends com.android.settingslib.Utils {
     /** Whether or not app hibernation is enabled on the device **/
     public static final String PROPERTY_APP_HIBERNATION_ENABLED = "app_hibernation_enabled";
 
+    /** Whether or not app hibernation targets apps that target a pre-S SDK **/
+    public static final String PROPERTY_HIBERNATION_TARGETS_PRE_S_APPS =
+            "app_hibernation_targets_pre_s_apps";
+
     /** Whether or not Settings Shared Axis transition is enabled */
     public static final String SETTINGS_SHARED_AXIS_ENABLED = "settings_shared_axis_enabled";