Add ScrollTimeline Polyfill for Swipe Recognizer using a new CustomTimeline protocol

[sebmarkbage]

The React API is just that we now accept this protocol as an alternative to a native AnimationTimeline to be passed to startGestureTransition. This is specifically the DOM version.

interface CustomTimeline {
  currentTime: number;
  animate(animation: Animation): void | (() => void);
}

Instead, of passing this to the Animation that we start to control the View Transition keyframes, we instead inverse the control and pass the Animation to this one. It lets any custom implementation drive the updates. It can do so by updating the time every frame or letting it run a time based animation (such as momentum scroll).

In this case I added a basic polyfill for ScrollTimeline in the example but we'll need a better one.

[react-sizebot]

Comparing: a947eba...e4bb93c

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	530.57 kB	530.57 kB	=	93.67 kB	93.67 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	+0.12%	651.66 kB	652.47 kB	+0.15%	114.78 kB	114.96 kB
facebook-www/ReactDOM-prod.classic.js	=	674.81 kB	674.81 kB	=	118.78 kB	118.78 kB
facebook-www/ReactDOM-prod.modern.js	=	665.30 kB	665.30 kB	=	117.19 kB	117.19 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against e4bb93c

[sebmarkbage]

This is also how you'd implement other gestures that can't be modeled as scroll. Such as rotate and zoom gestures.

[sebmarkbage]

I published this as a third party package instead since it's generally useful and I can put more complex ones there.

https://www.npmjs.com/package/animation-timelines