[MRESOLVER-431] Make chained repository and transfer listeners extens…

…ible (#361)

Add ability to extend classes.

---

https://issues.apache.org/jira/browse/MRESOLVER-431

maven-resolver-util/src/main/java/org/eclipse/aether/util/listener/ChainedRepositoryListener.java

@@ -33,7 +33,7 @@
  * A repository listener that delegates to zero or more other listeners (multicast). The list of target listeners is
  * thread-safe, i.e. target listeners can be added or removed by any thread at any time.
  */
-public final class ChainedRepositoryListener extends AbstractRepositoryListener {
+public class ChainedRepositoryListener extends AbstractRepositoryListener {
 
     private final List<RepositoryListener> listeners = new CopyOnWriteArrayList<>();
 
@@ -110,6 +110,9 @@ public void remove(RepositoryListener listener) {
         }
     }
 
+    /**
+     * Invoked when any listener throws, by default is no op, extend if required.
+     */
     @SuppressWarnings("EmptyMethod")
     protected void handleError(RepositoryEvent event, RepositoryListener listener, RuntimeException error) {
         // default just swallows errors

maven-resolver-util/src/main/java/org/eclipse/aether/util/listener/ChainedTransferListener.java

@@ -34,7 +34,7 @@
  * A transfer listener that delegates to zero or more other listeners (multicast). The list of target listeners is
  * thread-safe, i.e. target listeners can be added or removed by any thread at any time.
  */
-public final class ChainedTransferListener extends AbstractTransferListener {
+public class ChainedTransferListener extends AbstractTransferListener {
 
     private final List<TransferListener> listeners = new CopyOnWriteArrayList<>();
 
@@ -111,6 +111,9 @@ public void remove(TransferListener listener) {
         }
     }
 
+    /**
+     * Invoked when any listener throws, by default is no op, extend if required.
+     */
     @SuppressWarnings("EmptyMethod")
     protected void handleError(TransferEvent event, TransferListener listener, RuntimeException error) {
         // default just swallows errors