* DestinationCache is now synchronized on multiple 'destination' locks
(previously a single shared lock)
* DestinationCache keeps destinations without any subscriptions
(previously such destinations were recomputed over and over)
* SessionSubscriptionRegistry is now a
'sessionId -> subscriptionId -> (destination,selector)' map
for faster lookups
(previously 'sessionId -> destination -> set of (subscriptionId,selector)')
closes gh-24395
524ca1a676