Moving AppStandbyController to the module background thread.

Move AppStandbyController's handler to use the JS mainline module's
background thread looper to decouple it from the rest of the system and
from BackgroundThread.

Bug: 160873128
Test: atest CtsUsageStatsTestCases:UsageStatsTest
Test: atest FrameworksServicesTests:AppIdleHistoryTests
Test: atest FrameworksServicesTests:AppStandbyControllerTes
Change-Id: Ic64ccf6b4437060cb4ea83b1c5c6053421081ef8