Add willChangeFromState to views-dom

[appsforartists]

There should be a common way to set willChange$ from a state$. If #235 doesn't happen, we should have something like this:

function willChangeFromState(motionState$, activeName = 'transform')

If #235 does, this effectively becomes rewriteWhenTrue.

(See also #240 for the opacity:pointerEvents equivalent)