Notify the registered AutofillCallback for inline.

AutofillInlineSuggestionsRequestSession controls the inline
communication with the IME, we can centralize the UI show and hide
notification here. Use a variable mPreviousHasNonPinSuggestionShow to
save the previous status, when the display status change, e.g. from
no suggestion to has suggestions we can notify inline ui shown event.

Bug: 157762527
Test: atest android.autofillservice.cts.inline
Test: atest CtsAutoFillServiceTestCases:DatasetFilteringDropdownTest
Test: atest CtsAutoFillServiceTestCases:InlineFilteringTest
Test: atest CtsAutoFillServiceTestCases:LoginActivityTest
Test: Manual. Write a test app and register AutofillCallback, make
sure the callback is called as expected.

Change-Id: I8ee38008874c4a6f110635e8e4107a4eef72ed14