Autofill settings: Fix search

Ia012232ba2856e0757289982bc3045d948ff4aa8 replace the "Autofill service"
preference title with the earlier summary string. The change in title
causes search to not find the preference anymore. This change adds back
the title in xml, which makes search find it again. The Controller code
still overwrites the title with the application name.

Also fixes DefaultAutofillPreferenceControllerTest.

Bug: 192403526
Test: manual - clear Settings Services storage -> search "fill" -> click
 link
Test: make -j64 RunSettingsRoboTests \
 ROBOTEST_FILTER="com.android.settings.applications.defaultapps.DefaultAutofillPreferenceControllerTest"
Change-Id: I9714b3efd2a5a7d9ee7eef345415fa020ef0dc61