Make the fragment title can’t searchable

we shouldn't take users so deep into the settings IA because it's easy
to feel lost in settings after clicking on a result without additional
context.

Bug: 143055215
Test: robotest & manual
Change-Id: I337cb5ead31e1e4e7bf9be78132e90630f83ee43

tests/robotests/src/com/android/settings/gestures/AssistGestureSettingsTest.java

@@ -72,6 +72,6 @@ public class AssistGestureSettingsTest {
 
         assertThat(AssistGestureSettings.SEARCH_INDEX_DATA_PROVIDER.getNonIndexableKeys(
                 RuntimeEnvironment.application))
-                .contains("gesture_assist_settings_page");
+                .isNotEmpty();
     }
 }