Introduce a finer lock for JobNotificationCoordinator.

Introduce a new lock for local objects in JobNotificationCoordinator
which are not dependent on other JobScheduler objects. This will allow
for external services like NotificationManagerService to query the
relevant information in JobNotificationCoordinator without JS having to
hold the global lock and causing a deadlock.

Also update NonNull annotations.

Bug: 277694892
Test: atest JobNotificationCoordinatorTest
Test: atest NotificationTest
Test: atest NotificationManagerTest
Change-Id: I17013deb4c71b70a560c8f27e6186396012362e3