A live window with changing duration can't be properly
displayed in a media notification. The duration constantly
changes and creates a nervous jumping seekbar that is not
really useful.
This change sets the duration for live streams to `C.TIME_UNSET`
when publishing the player state to the platform session. This
way no duration is sent to the platform session which prevents
media controls from drawing a seekbar.
Issue: androidx/media#1256
PiperOrigin-RevId: 624112541
fc1d60beb9