Moar AutoFill Framework refactoring...

* Encapsulated application-level auto-fill logic on AutoFillSession.
  Currently, Activity.java directly manages the IAutoFillCallback binder
  object used to auto-fill its views, but this logic need to be
  extended so Views can use it to draw the auto-fill bar.

* Pass auto-fill id and boundaries to requests
  So AutoFillUI can display its affordance in the right places.

* Uses a new auto-fill id on View (instead of reusing accessibility's).
  That allows moving the logic on whether a new request should be made or
  the existing UI moved to the service side.

* Split service methods in 2, for shell cmd and app
  And applied the right permission check on both.

* Removed CancelationSignal from onSaveRequest()
  Since it's not really needed.

* Etc...
  ¯\_(ツ)_/¯

BUG: 34637800
BUG: 31001899
Test: CtsAutoFillServiceTestCases passes
Test: manual verification

Change-Id: Ibd0cb2cfff6d0f6bb6b697a423ed5e89df687b82