don't bubble object3dset/remove events

[ngokevin]

Description:

I think there's potential for surprise if we're listening to an object3dset event, and accidentally catch an object3dset event from a child. One would have to know to check the event target, which is unlikely to remember.

Changes proposed:

• Don't bubble object3dset/remove events.

[donmccurdy]

I'm not sure about this change. There are side effects:

1. No reliable way to listen for a new mesh entering the scene. Can try model-loaded, but you'll miss primitive geometries. Can try child-attached, but you'll get noise from entities that haven't finished loading, or that aren't intended to contain meshes.
2. The new raycaster refresh logic relies on this event reaching the scene, and will break with this change.

The risk of catching object3dset from children is real too, of course, but at least it's a risk that we share with most DOM APIs. Better the devil you know, etc.

[ngokevin]

That's true. I think we can revert then, especially given the raycaster refresh logic. Too bad the tests missed that, good catch.