Tracking Issue: Animation

Previously discussed in #1601.

- [x] Avoiding constant folding (#2232)
Progress on animation was stalled because of the constant folding: non-async secondary inputs are all evaluated as the graph is compiled.

- [x] Parametric animation (#2443)
Allow the time from the context to be retrieved by the user in the node graph via the "Animation Time" and "Real Time" nodes. Add simple buttons and keybinds for pausing/playing and restarting the animation.

- [ ] Add nodes for [easings](https://easings.net/)

- [ ] Implement the Timeline panel

- [ ] Add the ability to expose channels for keyframing from the Properties panel

- [ ] Onion skins

- [ ] 2D rigging