Review fixes for jetty-httpclient-12.0:library (open-telemetry#18074)

Author: otelbot[bot]

instrumentation/jetty-httpclient/jetty-httpclient-12.0/library/src/main/java/io/opentelemetry/instrumentation/jetty/httpclient/v12_0/TracingHttpClient.java

@@ -52,6 +52,8 @@ static TracingHttpClient buildNew(
           new TracingHttpClient(instrumenter, httpClientTransport, sslContextFactory);
     } else if (sslContextFactory != null) {
       tracingHttpClient = new TracingHttpClient(instrumenter, sslContextFactory);
+    } else if (httpClientTransport != null) {
+      tracingHttpClient = new TracingHttpClient(instrumenter, httpClientTransport);
     } else {
       tracingHttpClient = new TracingHttpClient(instrumenter);
     }

instrumentation/jetty-httpclient/jetty-httpclient-12.0/library/src/test/java/io/opentelemetry/instrumentation/jetty/httpclient/v12_0/JettyHttpClient12LibraryTest.java

@@ -11,6 +11,7 @@
 import io.opentelemetry.instrumentation.testing.junit.http.AbstractHttpClientTest;
 import io.opentelemetry.instrumentation.testing.junit.http.HttpClientInstrumentationExtension;
 import org.eclipse.jetty.client.HttpClient;
+import org.eclipse.jetty.client.transport.HttpClientTransportOverHTTP;
 import org.eclipse.jetty.util.ssl.SslContextFactory;
 import org.junit.jupiter.api.extension.RegisterExtension;
 
@@ -28,10 +29,13 @@ protected HttpClient createStandardClient() {
         .createHttpClient();
   }
 
+  // exercises the createHttpClient(HttpClientTransport) entry point as well
   @Override
   protected HttpClient createHttpsClient(SslContextFactory.Client sslContextFactory) {
     HttpClient client =
-        JettyClientTelemetry.builder(testing.getOpenTelemetry()).build().createHttpClient();
+        JettyClientTelemetry.builder(testing.getOpenTelemetry())
+            .build()
+            .createHttpClient(new HttpClientTransportOverHTTP());
     client.setSslContextFactory(sslContextFactory);
     return client;
   }