Moar pre-partitioning refactoring.

On ViewState: split value into mCurrentValue and mAutofilledValue.
On Session: replacing mAutofilledDataset by mDatasetWaitingAuth and
            ViewState.getAutofilledValue() (mAutofilledDataset is still needed,
	    but will be removed in the first partitioning CL).

Also fixed a missed 'return' on TimePicker.autofill()

Bug: 35707731
Test: CtsAutoFillServiceTestCases pass

Change-Id: Icc32701ae3e499a77d99e6ae1daa7d070a3df631