Add two MetadataRenderer instances by default

To receive multiple schemes of metadata emitted by a stream, multiple
`MetadataRenderer` instances need to be used. This change makes
`DefaultRenderersFactory` add two metadata renderers by default.

PiperOrigin-RevId: 715790821

RELEASENOTES.md

@@ -16,6 +16,9 @@
         items during playback to reduce media item transition latency.
     *   Fix issue where additional decode-only frames may be displayed in quick
         succession when transitioning to content media after a mid-roll ad.
+    *   Make `DefaultRenderersFactory` add two `MetadataRenderer` instances by
+        default to enable apps to receive two different schemes of metadata by
+        default.
 *   Transformer:
     *   Enable support for Android platform diagnostics via
         `MediaMetricsManager`. Transformer will forward editing events and

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/DefaultRenderersFactory.java

@@ -650,6 +650,7 @@ public class DefaultRenderersFactory implements RenderersFactory {
       @ExtensionRendererMode int extensionRendererMode,
       ArrayList<Renderer> out) {
     out.add(new MetadataRenderer(output, outputLooper));
+    out.add(new MetadataRenderer(output, outputLooper));
   }
 
   /**