Replace AutoFillType by view constants.

Now that AutoFillType does have any logic (since the "subType" logic was moved
to AutoFillHint), it makes more sense to get rid of the type and use constants
directly.

This change creates the contants and "pseudo-deprecate" the old stuff: it's
still available because some clients are using it, but it will be removed once
they migrate.

Bug: 35956626
Test: CtsAutoFillServiceTestCases pass

Change-Id: I0efe7f0cc101c86164a18c85903bb871e1f13ba2