Suppress prevent ringer gesture parent page in search.

The full page verion of prevent ringing is still searchable.

- Created a new controller for parent entry.
- On the child controller, inherit the same getAvailabilityStatus() but
  override AVILABLE_UNSEARCHABLE to AVAILABLE so it becomes searchable.

Fixes: 72748524
Test: existing robotests for PreventRingingPreferenceController

Change-Id: Id2454db110c81b59fa4a98338602b03de0812f8a
diff --git a/res/xml/gestures.xml b/res/xml/gestures.xml
index 650b1c4..9f69102 100644
--- a/res/xml/gestures.xml
+++ b/res/xml/gestures.xml
@@ -67,6 +67,6 @@
         android:key="gesture_prevent_ringing_summary"
         android:title="@string/gesture_prevent_ringing_screen_title"
         android:fragment="com.android.settings.gestures.PreventRingingGestureSettings"
-        settings:controller="com.android.settings.gestures.PreventRingingPreferenceController" />
+        settings:controller="com.android.settings.gestures.PreventRingingParentPreferenceController" />
 
 </PreferenceScreen>