Reusing the remote inline suggestion view during autofill filtering

* This gets rid of the flicker in the sample keyboard for most of
  tiem time, during filtering.
* We introduce a new object InlineFillUi to store the autofill
  inline candidates returned from the autofill provider. Filtering
  is applied internally to ensure a single place managing
  generating the InlineSuggestionsResponse that is sent to the IME.
  This enables us to reuse the backing remote view for filtering.
* The InlineFillUi is stored in the SessionController.
* The other classes within the UI package are marked as package
  private.
* Also implement the reference count to track the right time for
  releasing the remote view.

Test: atest android.autofillservice.cts.inline (sanity test)

Bug: 151467650
Change-Id: I023bd8cf8acf838088fba2d1d97c0e78d563222e