Add javadoc for Bundleable CREATOR fields

It's to comply with style guide as they are public.

PiperOrigin-RevId: 360914363

library/common/src/main/java/com/google/android/exoplayer2/audio/AudioAttributes.java

@@ -187,6 +187,7 @@ public final class AudioAttributes implements Bundleable {
     return bundle;
   }
 
+  /** Object that can restore {@link AudioAttributes} from a {@link Bundle}. */
   public static final Creator<AudioAttributes> CREATOR =
       bundle -> {
         Builder builder = new Builder();

library/common/src/main/java/com/google/android/exoplayer2/device/DeviceInfo.java

@@ -103,6 +103,7 @@ public final class DeviceInfo implements Bundleable {
     return bundle;
   }
 
+  /** Object that can restore {@link DeviceInfo} from a {@link Bundle}. */
   public static final Creator<DeviceInfo> CREATOR =
       bundle -> {
         int playbackType =