YAMAFFR - Yet Another Major AutoFill Framework Refactoring

- Explicitly split View methods into Assist and AutoFill methods, rather
  than use an overloaded method that takes flags.
- Simarly, renamed ASSIST_FLAG_SANITIZED_TEXT and
  ASSIST_FLAG_NON_SANITIZED_TEXT flags to
  AUTO_FILL_FLAG_TYPE_FILL and AUTO_FILL_FLAG_TYPE_SAVE respectively.
- Created a AutoFillUI class to host the auto-fill bar and other UI
  affordances.
- Moved the temporary notifications to AutoFillUI (eventually that
  class will host the real UI).
- Moved FillData to android.app.view.autofill package.
- Split IAutoFillCallback in 2 (IAutoFillAppCallback and
  IAutoFillServerCallback, residing at the app and system_server
  respectively), so service cannot fill the app directly (which lets
  the framework control the UI).
- Moved assist's IResultReceiver to AutoFillServiceImpl so
  system_server can act as a mediator between the AutoFillService
  implementation and the app being auto-filled.
- Replaced FillData and FillableInputFields by a bunch of new objects:
  - FillResponse contains a group of Datasets, each representing
  different values
    that can be used to auto-fill an activity (for example, different
    user accounts), optional id of fields the service is interested
    to save, and an optional bundle for service-side extras.
  - Dataset contains a name, Fields, and an optional bundle for
    service-side extras.
  - Fields contain an AutoFillId (parcelable) and a value (Bundle)
- Changed the temporary notifications to emulate the new workflow:
  - Initial notification requests the auto-fill data but do not
    auto-fill.
  - Once service calls back, a new notification is shown with the
    results.
  - Then if the user selects a dataset, the activity is auto-filled
    with it.
  - It also shows a notification to emulate what can be saved.
- Created an VirtualViewDelegate for views that uses a virtual
  hierarchy for assist data.
- Added new methods on ViewStructure to add children with virtual ids.
- Added 2 methods on View to support auto-fill:
  - autoFill(Bundle) to auto-fill the view.
  - getAutoFillType() to return how the view can be auto-filled.
- AutoFillType defines the input fields that support auto-fill:
  - Text fields (like EditText)
  - Toggle fields (like CheckBox)
  - Lists (like RadioGroup)
- AutoFillType can also have a sub-type representing its semantic (for
  now only text fields have it, and it's the same as getInputType()).
- etc :-)

Bug: 31001899
Test: manual verification
Change-Id: I2dd2fdedcb3ecd1e4403f9c32fa644cb914e186f