SDK / exoplayer

Adding items to an empty playlist is slightly different from adding
items to a non-empty playlist, because the former usually requires to
handle a change in the current item, position and playback state,
while the latter is not expected to affect the current item, position
or state.

The current ExoPlayer and SimpleBasePlayer code doesn't account for
this difference, leading to inconsistent behavior between
setMediaItem(s) and addMediaItem(s) when called on an empty playlist.

PiperOrigin-RevId: 530549928