Refactored Autofill to move starting flag out of Session.

Otherwise, all onFillRequest() calls in the same partition would use
the same flags.

Fixes: 37675138
Test: existing CtsAutoFillServiceTestCases pass
Test: CtsAssistTestCases pass
Test: PartitionedActivityTest.testAutofill4ParitionsMixManualAndAuto() pass

Change-Id: I03c8a036637bae534904d4f41265e451088cf940
10 files changed