Add service-state content provider

Add the ServiceStateProvider which clients can use to get the current
ServiceState given a subId and be notified when the service state
changes.

Test: runtest --path ServiceStateProviderTest.java
Bug: 33756364
Change-Id: Iecfee79fca45accbf701bc7729229c60ecc0cdbb
Merged-In: Iecfee79fca45accbf701bc7729229c60ecc0cdbb
5 files changed