[REQUIRED] Use case description

Thank you for supporting the Media3 Compose UI version!

The Timebar is an essential feature in ExoPlayer, and having it in the demo would be really helpful. It would give developers a clearer understanding of how to use it in a Compose-based setup.

Would you consider adding it? Thanks!

Proposed solution

Add a new TimebarState, similar to other state implementations, to allow better control and interaction with the Timebar.

Alternatives considered

N/A