Control operation handles

Back to Use gameplay actions.

Lua handles use dot or colon calls; JavaScript/Python use member calls. onFinished registers a completion function, state() reports status/error (Gameplay.state(handle) in C), and pause, resume, cancel, reverse control an operation. Reverse is supported on tween/value/move/lookAt/path/orbit/wait, not sequence/parallel/follow/shake. Cancel does not call completion. Completed state history is bounded to 1024 operations. The scene supports at most 8192 retained operations (up to 65536 aggregate action nodes), 4096 subscriptions, and 4096 queued callbacks per queue.