Move LOCK_TO_APP_EXIT_LOCKED from System to Secure

To prepare for controlling from settings.

While here, add lock to app settings to backups.

Bug: 16957435
Change-Id: I059140cd07a7a0d5ceb4e0bfe5e0176cb96629d3
diff --git a/services/core/java/com/android/server/am/ActivityStackSupervisor.java b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
index c1bf955..dfbdfce 100644
--- a/services/core/java/com/android/server/am/ActivityStackSupervisor.java
+++ b/services/core/java/com/android/server/am/ActivityStackSupervisor.java
@@ -3550,9 +3550,9 @@
                         }
                         mLockTaskNotify.show(false);
                         try {
-                            boolean shouldLockKeyguard = Settings.System.getInt(
+                            boolean shouldLockKeyguard = Settings.Secure.getInt(
                                     mService.mContext.getContentResolver(),
-                                    Settings.System.LOCK_TO_APP_EXIT_LOCKED) != 0;
+                                    Settings.Secure.LOCK_TO_APP_EXIT_LOCKED) != 0;
                             if (!mLockTaskIsLocked && shouldLockKeyguard) {
                                 mWindowManager.lockNow(null);
                                 mWindowManager.dismissKeyguard();