Adds support for tracking position state in a media session. The position state is a combination of the playback rate, duration and current playback time. This can then be used by browsers to display position in the UI and with the addition of seeking can support seeking/scrubbing too. By default, the position state is taken from the media element. However, this does not work in all cases and therefore this provides a setPositionState() method to the site to specify a custom position state.
We should add support for tracking position state since this is supported by the platform and allows sites to provide a better experience.
Docs: N/A
Explainers: https://github.com/WICG/mediasession/blob/master/explainer.md