Make CHANGE_APP_IDLE_STATE a system API

Allows a privileged app to set standby bucket states for apps.

Bug: 63527785
Test: adb shell am set-standby-bucket com.example.foo 0
Change-Id: I613f8872ae816e39b167aad1c289187362aa6094
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 77bfec3..4a4de24 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -3062,10 +3062,10 @@
         android:protectionLevel="signature|privileged|development|appop" />
     <uses-permission android:name="android.permission.PACKAGE_USAGE_STATS" />
 
-    <!-- @hide Allows an application to change the app idle state of an app.
+    <!-- @hide @SystemApi Allows an application to change the app idle state of an app.
          <p>Not for use by third-party applications. -->
     <permission android:name="android.permission.CHANGE_APP_IDLE_STATE"
-        android:protectionLevel="signature" />
+        android:protectionLevel="signature|privileged" />
 
     <!-- @hide @SystemApi Allows an application to temporarily whitelist an inactive app to
          access the network and acquire wakelocks.