fix: improve derivation of style for controller.set

[parkerziegler]

This PR is a small but important one! It improves the way we derive a from style to use for animations set off by controller.set. The algorithm, with this change, becomes:

• Look at the currently applied style property of the animating element.
• If there's a matching value for the to property specified in controller.set, use that value. It's very likely this value will have been set by a previous run of a renature animation.
• If there is not a matching value for the to property specified in controller.set, use the computed value. Computed values are always specified in px, so this is still an edge case where our animations fall a bit short. Would love for community contributors to help out with this piece!

This brings us more in parity with how d3 works, which is our sample reference point for this behind the scenes style derivation.