[JobScheduler] Refactored CarIdlenessTracker to add clarity

Added protected-broadcast for 4 actions that will be used by Car
service:
* com.android.server.jobscheduler.GARAGE_MODE_ON
* com.android.server.jobscheduler.GARAGE_MODE_OFF
* com.android.server.jobscheduler.FORCE_IDLE
* com.android.server.jobscheduler.UNFORCE_IDLE

Test: WIP
Bug: 111552186
Change-Id: Ifa6729db38f32479f06e814a713ba9e2b419f88f