These events are always reported with the primary child period ID,
because this is the same ID used in the parent `MergingMediaSource`'s
Timeline.
This ensures that e.g. loading errors from sideloaded subtitles (which
uses `MergingMediaSource`) are now reported via
`AnalyticsListener.onLoadError`.
It results in non-error events being reported from these children too,
which will result in more `onLoadStarted` and `onLoadCompleted` events
being reported (one for each child).
Issue: androidx/media#1722
PiperOrigin-RevId: 686901439
191bc094a5