Settings search - Navigate user to exact page

- remove duplicate index preference
- default set searchable = false when the preference has fragment
- make some fragments indexable

Bug: 143057584
Test: robotest & manual

Change-Id: I4d64f6106d2f92f0a45e8c7e26388677f593f412

res/xml/accessibility_shortcut_service_settings.xml

@@ -17,4 +17,5 @@
 
 <PreferenceScreen
     xmlns:android="http://schemas.android.com/apk/res/android"
+    android:key="accessibility_shortcut_service_screen"
     android:title="@string/accessibility_shortcut_service_title" />