Add a way to read the last AutofillSelection.

- Check UID to make sure one service cannot read FillSelections of other
  services
- Add id to Dataset to allow to tag the datasets. This id is then found
  in the FillSelection.Event
- Add clientState to FillSelection to allow service to store more data

Fixes: 36871500
Test: CtsAutoFillServiceTestCases
Change-Id: Ice894245508227265294a1c59ea97842175e5aec