Add a few pages to search index.

- Data saver
- A few special permission access pages
   - Picture-in-picture
   - Premium sms
   - do not disturb access
- And a unrelated cleanup: move EmptyTextFragment from
  notification/ to widget/

Bug: 70720645
Test: robotests
Change-Id: I6a87f712bf81f9fd32fa9a3826fba851ca748409