Support querying UsageStatsManager in SystemUI

Adds a new repository and corresponding interactor to allow SystemUI to
query UsageStatsManager. Only activity events are supported.

Test: atest UsageStatsInteractorTest
Test: atest UsageStatsRepositoryTest
Flag: EXEMPT new code is unused
Bug: 350468769
Change-Id: I36ba083cb66ea146107123f8b5260ff8391b2483