SDK / exoplayer

This includes:

- Add an ad for each LOADED event of the SDK by taking the duration
  of the ad from the media structure to exactly match the start position
  of ads and then use `addLiveAdBreak()` that is used for HLS live already.
- When the refreshed content timeline arrives, possibly correct
  the duration of an ad that has been inserted while the period duration was
  still unknown (last period of the live timeline).
- When an ad period is removed the ad group needs to be put into a condition
  that allows continuing playback.

PiperOrigin-RevId: 520919236