GUP: Display a list of Apps and dialogs

1) Add preference controller for gup dashboard and add list preferences
for each entry of the apps
2) Add gup dashboard page to search index
3) Add comprehensive tests for GupPreferenceController

Bug: 119221883
Test: make RunSettingsRoboTests
Change-Id: Ide4934c0dd3901532723e77e74663e5a7b639026