Make LLUDPServer.Scene publicly gettable/privately settable instead of protected so that other logging code in the clientstack can record more useful information

Adds some commented out logging for use again in the future.
No functional change.
Add experimental OutgoingQueueRefillEngine to handle queue refill processing on a controlled number of threads rather than the threadpool.

Disabled by default.  Currently can only be enabled with console "debug lludp oqre start" command, though this can be started and stopped whilst simulator is running.
When a connection requires packet queue refill processing (used to populate queues with entity updates, entity prop updates and image queue updates), this is done via Threadpool requests.
However, with a very high number of connections (e.g. 100 root + 300 child) a very large number of simultaneous requests may be causing performance issues.
This commit adds an experimental engine for processing these requests from a queue with a persistent thread instead.
Unlike inbound processing, there are no network requests in this processing that might hold the thread up for a long time.
Early implementation - currently only one thread which may (or may not) get overloaded with requests.  Added for testing purposes.
Add clientstack.<scene>.OQRERequestsWaiting stat

Only present if OQRE is enabled
minor:Give console feedback when we sit or stand pCampbot bots.

Also only write console lines for actually connected bots.
Add "debug lludp drop out <add|remove> <packet-name>" console command for debug/test purposes.

This drops all outbound packets that match a given packet name.
Can currently only be applied to all connections in a scene.
Extend drop command to "debug lludp drop <in|out>..." to allow drop of inbound packets.

For test/debug purposes.
BulletSim: add new Bullet 2.82 constraint type codes and rename the
BulletSim fixed constraint to not be confused with the native version.
Fix typo in OpenSimDefaults.ini comment
Merge branch 'master' into bullet-2.82