Add API to get hibernation eligibility

Add an API to get a package's eligibility for hibernation for a given
user. A package is either eligible, exempt by the system, or exempt by
the user.

This information can be used to show more accurate UI for hibernation
controls (e.g. disabling the user-controlled exemption toggle if the app
is already exempt by the system)

Bug: 200087723
Test: CTS test in topic
Change-Id: Iea844477184fadb55ea14485dff172ed7be2b715