
Before this change: - SimpleExoPlayer.prepare(mediaSource) ended up calling ExoPlayerImpl.setMediaSourcesInternal() with startWindowIndex=0 and resetToDefaultPosition=false. - ExoPlayerImpl.prepare(mediaSource) ended up calling ExoPlayerImpl.setMediaSourcesInternal() with startWindowIndex=C.INDEX_UNSET and resetToDefaultPosition=true. This was functionaly equivalent but a bit confusing. #minor-release PiperOrigin-RevId: 368818143