Change to drop down when the inline suggestions don't be shown in IME.

The current implementation has a problem where:
In the autofill side, there can be multiple autofill sessions existed
at the same time. But in the IME side, there is always only one
InlineSuggestionSession at any given time. It will cause the previous
autofill session to fail communication with IME.

It would better change to drop down UI when the autofill inline
suggestions don't be shown in IME.

How to reproduce this issue:
To add an input field with autofillable into the authentication activity
of InlineFillService. To tap on the input field of the authentication
activity during the authentication flow. After completing the
authentication, the inline suggestions won't be shown in IME.

BTW, if the input field is marked as non-autofillable, this issue won't
occur.

Manual verification:
1.Tested this patch with InlineFillService and it worked well.
2.Feng also helped to test this patch with the webview
(sort of randomly), and didn't find any broken case

Bug: 158877106
Test: atest CtsInputMethodTestCases
Test: atest CtsAutoFillServiceTestCases
Test: new CTS test Ie1d9055b0eabfcaa00861869467be8dcee25833e
Test: manual verification with InlineFillService
Test: Feng also helped to test this patch with the webview
Change-Id: Ib06edd823fa4478f34362164f3f7dd3544e51705