Improvements on ACTION_REQUEST_SET_AUTOFILL_SERVICE:

- Moved to proper package.
- Returns right away when:
  - AutofillService for package is already selected
  - Autofill is not available

Bug: 37576671
Bug: 37673809

Test: manual verification
Test: make RunSettingsRoboTests -j90

Merged-in: Icda260cea1b4ce6cdefd8eff9625b2b768a5ed86
Change-Id: Icda260cea1b4ce6cdefd8eff9625b2b768a5ed86