Clear inline suggestions before onStartInput instead of before onFinishInput

* In case where there are multiple input fields in a single WebView,
  switching focuses between input fields doesn't trigger an onFinishInput
  from the previous field. But it always triggers an onStartInput in
  the new field. So it's safer to clear the suggestions onStartInput

Test: atest android.autofillservice.cts.inline
Test: atest CtsInputMethodTestCases
Bug: 159479887
Bug: 157515522

Change-Id: Ie380db855fbc93600635790ef5adc1031d6f0787