Checks that prebundled categories contain only preinstalled contents.

Bug: 353888087
Test: atest AccessibilitySettingsTest
Test: manually check all prebundled services are still in their proper
      groups, even after installing an APK update
Flag: com.android.settings.accessibility.check_prebundled_is_preinstalled
Change-Id: I023db9c37d7990deb50c9eec516619f0a8db65b7

aconfig/accessibility/accessibility_flags.aconfig

@@ -20,6 +20,16 @@ flag {
   }
 }
 
+flag {
+  name: "check_prebundled_is_preinstalled"
+  namespace: "accessibility"
+  description: "Checks that all 'prebundled' components, used for grouping, are also preinstalled"
+  bug: "353888087"
+  metadata {
+    purpose: PURPOSE_BUGFIX
+  }
+}
+
 flag {
   name: "edit_shortcuts_in_full_screen"
   namespace: "accessibility"