Playability: imperative vs declarative control

When an area of DOM (or component subtree) becomes unrendered or uninteractive, we need to pause relevant components. Otherwise the playback will continue and use will have no way of finding where it’s coming from and how to stop it.

For playability we can use `AmpContext` context properties.

For imperative/declarative control, playback is very difficult to support declaratively. This we can use `useImperativeHandle` and export playback API including `playState`, `play`, `pause`, and other similar methods.