Split listener classes from SmtEngine (#4816)

Split listener classes from SmtEngine (#4816)

This moves listener classes owned by SmtEngine to their own file.

The SmtEnginePrivate class previously what itself a NodeManagerListener. This class will be deleted. Instead a new NodeManagerListener is introduced here whose sole responsibility is to do the work required for node manager listening.

Note I had to add a (temporary) friend relationship to SmtEngine, which will be removed in an upcoming PR to split the management of dumping to its own utility.