Fix Autofill's DATASETS_SHOWN event to be triggered when the UI shows,

instead of before.

Note: this also fixes cases in which DATASET_SHOWN events were logged
multiple times but only shown once.

Test: atest
* android.autofillservice.cts.inline.InlineFillEventHistoryTest
* android.autofillservice.cts.dropdown.FillEventHistoryTest
* manually test filldialog history

Bug: 230363706
Change-Id: I7076621490a64ef52b11180970494d4313936f69
Merged-In: I7076621490a64ef52b11180970494d4313936f69