Add charging parole notification for network changes.

This is a partial revert of the change to remove parole from
AppStandbyController (Ide382ad7fb9c7441f0a5232833ad39bf8c3a1e94). This
adds back the listener and notification of when parole (due to charging)
turns on and off so that NetworkPolicyManagerService can quickly update
the network policy for affected apps. AlarmManager and JobScheduler
already listen to charging status, so I'm excluding them from this
change to make it as simple and low-risk as possible.

This has a slight change to follow standard practice where a client
registering a listener retrieves the current value after registering
the listener instead of the registerListener() method calling the
listener's onStateChanged() method.

Bug: 151802309
Test: atest FrameworksServicesTests:AppStandbyControllerTests
Test: atest --rerun-until-failure 10 com.android.cts.net.HostsideRestrictBackgroundNetworkTests
Change-Id: I18d8d771d455456351e3a9a6c9469e4ec620ae4e