Spectate XRUI for remote players

[speigg]

We don't have a universal way of identifying entities (scene objects and/or network objects).

Proposal: register scene entities as network objects. Scene objects should be identifiable by the same owner/id convention used for spawning objects. Then, networked Interact actions can reference objects by that same convention.

[HexaField]

We should definitely implement proper XRUI pooling before doing this.