Add React utility hooks

[MattiasBuelens]

This adds hooks such as useCurrentTime(), usePaused() and useVolume(), to easily access the player's state from within a custom React component.

I also reworked our internals to avoid useEffect() as much as possible, using the techniques from You Might Not Need an Effect.

• Adding/removing event listeners now uses useSyncExternalStore.
• usePlayer() now accepts the UI element as a prop, rather than returning a setUi callback.