LPS-45309 Fix EhcachePortalCacheManager.getCacheManagerListeners().
LPS-45309 The underneath CacheManager could have other type of CacheManagerEventListener installed which needs to be filtered out
LPS-45309 To make the logic consistent, MemoryPortalCacheManager should also return a copied set of the CacheManagerListeners
LPS-45309 Because of the copy of CacheManagerListener, now it is necessary to expose a convenient method to unregister CacheManagerListeners
LPS-45309 SF