HTTPASYNC-173 - Expose a protected constructor in DefaultAsyncClientConnectionOperator and mark it @SInCE 5.6.

Author: arturobernalg

httpclient5/src/main/java/org/apache/hc/client5/http/impl/nio/DefaultAsyncClientConnectionOperator.java

@@ -71,7 +71,17 @@ public class DefaultAsyncClientConnectionOperator implements AsyncClientConnecti
     private final MultihomeIOSessionRequester sessionRequester;
     private final Lookup<TlsStrategy> tlsStrategyLookup;
 
-    DefaultAsyncClientConnectionOperator(
+    /**
+     * Constructs a new {@code DefaultAsyncClientConnectionOperator}.
+     *
+     * <p><strong>Note:</strong> this class is marked {@code @Internal}; rely on it
+     * only if you are prepared for incompatible changes in a future major
+     * release.  Typical client code should use the high-level builders in
+     * {@code HttpAsyncClients} instead.</p>
+     *
+     * @since 5.6
+     */
+    protected DefaultAsyncClientConnectionOperator(
             final Lookup<TlsStrategy> tlsStrategyLookup,
             final SchemePortResolver schemePortResolver,
             final DnsResolver dnsResolver) {