Cross-platform: ManagedPlayer plugins API

[Rafael Campos]

Problem

We leverage the ManagedPlayer to handle multi-flow. However, we don't expose its state/methods through a plugin API.

Therefore, although we can leverage middleware, we can't inspect its state or react to its lifecycle, but only to the wrapped Player instance.

Solution

Follow the current Player approach, adding a plugin API to the ManagedPlayer so users can enhance, inspect, or modify its behaviour and state.