Build a reactive property inspector UI

[jverkoey]

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Building upon the same algorithm that generates our graphviz representation, we can enumerate every reactive property that is connected to the runtime and generate a UI for tweaking these properties in real time.

The applications of this expand beyond motion, even.

For example, to make cornerRadius tweakable:

let cornerRadius = createProperty(withInitialValue: 5)
runtime.connect(cornerRadius, to: runtime.get(view.layer).cornerRadius)

[jverkoey]

Related to https://github.com/material-motion/material-motion-swift/issues/88.