Mark AdaptiveTrackSelection.AdaptationCheckpoint as public

The protected visibility causes problems in Kotlin (Issue: #8830) and
also prevents a subclass of AdaptiveTrackSelection.Factory that isn't
nested inside a subclass of AdaptiveTrackSelection (in both Java and
Kotlin).

#minor-release

PiperOrigin-RevId: 369468841

RELEASENOTES.md

@@ -42,6 +42,10 @@
         get notified after MediaCodec is initialized, or they can inject a
         custom `MediaCodecAdapter.Factory` if they want to control how the
         `MediaCodec` is configured.
+    *   Promote `AdaptiveTrackSelection.AdaptationCheckpoint` to `public`
+        visibility in order to allow Kotlin subclasses of
+        `AdaptiveTrackSelection.Factory`
+        ([#8830](https://github.com/google/ExoPlayer/issues/8830)).
 *   UI:
     *   Add builder for `PlayerNotificationManager`.
     *   Add group setting to `PlayerNotificationManager`.

library/core/src/main/java/com/google/android/exoplayer2/trackselection/AdaptiveTrackSelection.java

@@ -697,7 +697,7 @@ private static void addCheckpoint(
   }
 
   /** Checkpoint to determine allocated bandwidth. */
-  protected static final class AdaptationCheckpoint {
+  public static final class AdaptationCheckpoint {
 
     /** Total bandwidth in bits per second at which this checkpoint applies. */
     public final long totalBandwidth;