Make values forwarded to bandwidth listener final again.

When notifying the bandwidth listeners of new samples, the forwarded values
need to be final to prevent concurrent access. Putting the event forwarding
into a separate method ensures the values are final.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=204877650

library/core/src/main/java/com/google/android/exoplayer2/upstream/DefaultBandwidthMeter.java

@@ -226,13 +226,14 @@ public final class DefaultBandwidthMeter implements BandwidthMeter, TransferList
         bitrateEstimate = (long) slidingPercentile.getPercentile(0.5f);
       }
     }
-    eventDispatcher.dispatch(
-        listener ->
-            listener.onBandwidthSample(
-                sampleElapsedTimeMs, sampleBytesTransferred, bitrateEstimate));
+    notifyBandwidthSample(sampleElapsedTimeMs, sampleBytesTransferred, bitrateEstimate);
     if (--streamCount > 0) {
       sampleStartTimeMs = nowMs;
     }
     sampleBytesTransferred = 0;
   }
+
+  private void notifyBandwidthSample(int elapsedMs, long bytes, long bitrate) {
+    eventDispatcher.dispatch(listener -> listener.onBandwidthSample(elapsedMs, bytes, bitrate));
+  }
 }