Add: Smoothing (Alternative to animation)

[johannesvollmer]

It would be nice to make smoothing a native feature. I imagine something like CSS transitions, similar to the existing Viro animation API, but aimed towards smoothing continuously changing attributes (position, rotation, scale).

This could alternatively be implemented in user code, if Viro would offer an Update trigger (a frame-synchzonized callback, called on every frame, for smooth user-transitions).

I'm willing to contribute, what do you think?