Add container to Format.toLogString

While investigating Issue: androidx/media#887 I naively assumed the CEA-608
captions were in a TS file, but they're actually in an MP4 (which is
possibly obvious given DASH only supports MP4). This change includes
container info in the `EventLogger` `tracks` output.

PiperOrigin-RevId: 592192752

libraries/common/src/main/java/androidx/media3/common/Format.java

@@ -1232,6 +1232,9 @@ public final class Format implements Bundleable {
     }
     StringBuilder builder = new StringBuilder();
     builder.append("id=").append(format.id).append(", mimeType=").append(format.sampleMimeType);
+    if (format.containerMimeType != null) {
+      builder.append(", container=").append(format.containerMimeType);
+    }
     if (format.bitrate != NO_VALUE) {
       builder.append(", bitrate=").append(format.bitrate);
     }