Create a UsageEventListener.

Creating the UsageEventListener to generalize conveying new usage events
so that multiple components can be notified.

Bug: 142281756
Bug: 171305774
Test: atest AppIdleHostTest
Test: atest CtsUsageStatsTestCases:UsageStatsTest
Test: atest FrameworksMockingServicesTests:UsageStatsServiceTest
Test: atest FrameworksServicesTests:AppIdleHistoryTests
Test: atest FrameworksServicesTests:AppStandbyControllerTests
Change-Id: I176c476257600f0f4299a10f02b5c61332007b1c