-Updated MediaSource contracts in ManagedMediaSource.
-Changed PlaceholderMediaSource and FailedMediaSource to use built-in BaseMediaSource implementation.
-Changed deprecated DynamicConcatenatingMediaSource to ConcatenatingMediaSource.
-Removed manual playlist media source disposal in favor of player built-in disposal.
-Added sync buttons on live streams to allow seeking to live edge.
-Added custom cache key for extractor sources to allow more persistent reuse.
-Refactored player data source factories into own class and separating live and non-live data sources.