Explore equivalent to getSnapshotBeforeUpdate to fully cover React component API

[jsiwhitehead]

Apart from getSnapshotBeforeUpdate, Refluent has an equivalent for all of the React component API (including the new async rendering lifecycle methods), so it would be great to fill that last missing piece.

I've not personally needed it, so the first step would probably be finding some example use cases to explore how they might fit into the Refluent model.