[ntcore] Various NT4 fixes (#4474)

* TopicListener: Fix Add() return values
* Update PubSubOption poll storage documentation
* Update NetworkTableEntry::GetValue() doc
* Add documentation regarding asynchronous callbacks
* Unpublish entry: set publisher to nullptr
* Implement ValueListenerPoller default constructor
* Remove SetNetworkIdentity, make parameter to StartClient
* URI-escape client ID, improve error message
* Add connected message with client id; also improve disconnected message a bit
* Handle SetServers either before or after StartClient
* Fix client use-after-free; also delay reconnect after disconnect to rate limit
* Don't re-announce to already subscribed client; we especially don't want to send the last value again
* Always accept in-order sets, only use timestamp for tiebreak
* Fix LocalStorage::StartNetwork race
* Remove unused/unimplemented function

Also:
* [glass] Remove debug print
* [glass] Fix mpack string decoding
* [cameraserver] Fix up startclient

wpilibj/src/main/java/edu/wpi/first/wpilibj/RobotBase.java

@@ -144,7 +144,6 @@ public abstract class RobotBase implements AutoCloseable {
     m_threadId = Thread.currentThread().getId();
     setupCameraServerShared();
     setupMathShared();
-    inst.setNetworkIdentity("Robot");
     // subscribe to "" to force persistent values to progagate to local
     m_suball = new MultiSubscriber(inst, new String[] {""});
     if (isReal()) {