re-publicize InstancedGeometry no-arg constructor, correct erroneous javadoc

[stephengold]

Per post-merge discussion of PR #1228, I propose re-publicizing the no-arg constructors for InstancedGeometry, LightNode, and CameraNode. Also removing/correcting the javadoc for these classes (plus Geometry and Node) since the no-arg constructors are apparently NOT serialization-only.

[pspeed42]

Ok... so I looked into this deeper and I was wrong about CameraNode and LightNode. The way they are written, they are totally broken if you use the no-arg constructor so it should be protected. They internally use a control that is never created if you use the no-arg constructor. I'd argue that we should write them to be more flexible but I still think they are useless classes.

Sorry I didn't look at the whole class before commenting on them.

[stephengold]

Thanks for looking. I'll amend the PR.

[pspeed42]

Thanks. I was waiting on this to make the 3.3 branch. :)

[stephengold]

Huh. None of the other PRs seemed worth waiting for?

[pspeed42]

I mean, this one was influx. I wasn't going to cut a release until Sunday night and then couldn't find my notes on how to do it. When I found it on Monday, this was still going back and forth so I thought I'd wait.