Add StateTracker classes

One shared StateManager object will manage all StateTrackers across all configs, maintaining a map of atom ids to StateTrackers.

StateManager is responsible for initializing and removing StateTrackers and notifying them of event or StateListener changes.

Each StateTracker maintains a list of StateListeners and is responsible for tracking state values to primary keys and notifying StateListeners when a state change occurs.

Test: bit statsd_test:*
Bug: 136566566

Change-Id: Icb61c668a01b611aa75caa7bdc2a6801c650b119