Prepare PackageState/PackageUserState for API

Marks the applicable places as @hide. Only the immediate APIs
needed for the ART services integration will be exposed in the
first round. This makes review easier and isolates the changes.

Bug: 235462722

Test: m update-api with classes marked as API succeeds

Change-Id: I7850ea5b1deb479c596112f88c92f0045ebed743