Support synchronized live playback for HLS

[stevemayhew]

Use case description

Multiple Android TV streamers in a bar or other hospitality situation require video synchronized to a single live offset. This feature is documented in https://developer.android.com/guide/topics/media/exoplayer/live-streaming

The problem is this unlikely to work for HLS, as there is no spec mandated synchronization of time in the client to common time (NTP or the origin server). The spec does recommend msec accurate wall-clock time in the playlist:

#EXT-X-PROGRAM-DATE-TIME:

where date-time-msec is an ISO/IEC 8601:2004 [ISO_8601] date/time
representation, such as YYYY-MM-DDThh:mm:ss.SSSZ. It SHOULD indicate
a time zone and fractional parts of seconds, to millisecond accuracy.

So, all the pieces except for time synchronization are present.

Note, this is also requested in google/ExoPlayer#10990

Proposed solution

Simple, synchronize `androidx.media3.exoplayer.hls.HlsMediaSource.Factory#elapsedRealTimeOffsetMs

Alternatives considered

n/a