ISPN-3335 JMX statistics for Queries do not work after adding new classes to SearchFactory

In Infinispan we use SearchFactory reconfiguration when adding new classes. This process actually builds a new SearchFactory behind the scenes which should preserve all state and config of the old one, plus the new added classes.
Unfortunatelly this does not work correctly due to HSEARCH-1461. The statistics are lost on each reconfiguration. Also the the status of Statistics.isStatisticsEnabled is lost.

This is worked around by constructing a new MBean statistics implementtion, with identical interface. The new implementation accumulates its own statistics counters and gathers current data from the current Statistics object of the SearchFacotry.