[w3c/uievents] Reduce scroll performance impact of `wheel` listeners (#109)

`wheel` events are a big problem for scroll performance.  Eg. using [timestamps to monitor latency](http://rbyers.github.io/scroll-latency.html) @n8schloss has found that `wheel` listeners are a real problem for scroll performance in Facebook.  There are a number of incubation-style efforts underway to try to improve this, which if successful should probably make it back into the UIEvents specification somehow.

In particular:
- When all `wheel` listeners are [passive](https://github.com/WICG/EventListenerOptions/blob/gh-pages/explainer.md), wheel events should be uncancelable (already shipping in Chrome and I believe Safari and Firefox).
- Define touchpad "latching" and use that to [make wheel events uncancelable during a scroll](https://github.com/WICG/interventions/issues/33)
- Let developers [opt-out](https://bugs.chromium.org/p/chromium/issues/detail?id=162179#c75) of scrolling bubbling up past some elements (eg. fixed position), eliminating the need for some non-passive wheel listeners
- Define a declarative `wheel-action` API to make it easier to move to a passive-by-default model as [we're working towards for touch](https://github.com/WICG/interventions/issues/18).

/cc @tdresser @dtapuska @igrigorik


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