Add visibility migration helper and test.

We upgrade Visibility schema from version 0 to 1.
Version 0: one VisibilityDocument contains all visibility information
for whole package.
Version 1: One VisibilityDocument contains visibility information for
a single schema.

We need a migration plan to ensure upgrading devices won't lost
any information.

Test: VisibilityStoreMigrationHelperTest
Bug: 203736617
Change-Id: I405fe8c130d3c88a69ec4360a83b07faa33b6d0d
4 files changed