Major Description
Right now the PendingMessageCursor keeps track of the number of pending messages (the size() method). It would be useful to also report back the total message size besides just the count so we know how much memory or disk space is being used by pending messages.
Now that KahaDB is keeping track of the size of each message as of 5.12, it should be possible to report back this value in a non-blocking way. For a Queue this is pretty straightforward but for DurableSubscriptions some work will need to be done to keep track of the message size for unacked messages for each subscription.
