Add WebSocket upgrade test cases for JDK-8361305

[Copilot]

Adds test coverage for WebSocket upgrade behavior per JDK-8361305, which reports that direct WebSocket connections work but upgrades fail when HTTP/2 connections already exist to the same host.

Changes

• NettyWebSocketServer - Netty-based WebSocket server supporting both HTTP/1.1 and WebSocket protocols on the same port for test scenarios
• JavaHttpClientWebSocketTest - Two test cases:
  • testDirectWebSocketConnection() - Verifies ws:// URIs work with HttpClient.newWebSocketBuilder()
  • testWebSocketUpgradeAfterHttp2() - Tests WebSocket connection after HTTP request to same host:port

Test Behavior

// Test 1: Direct connection (works)
HttpClient client = HttpClient.newHttpClient();
WebSocket ws = client.newWebSocketBuilder()
    .buildAsync(URI.create("ws://localhost:8090/websocket"), listener)
    .get();

// Test 2: After HTTP connection to same host (documents JDK-8361305 scenario)
HttpClient client = HttpClient.newBuilder()
    .version(HttpClient.Version.HTTP_2)
    .build();
client.send(httpRequest, BodyHandlers.ofString());  // Establish HTTP connection
WebSocket ws = client.newWebSocketBuilder()
    .buildAsync(URI.create("ws://localhost:9090/websocket"), listener)
    .get();  // May fail per JDK-8361305

On Java 17.0.17, both scenarios pass, suggesting the issue may be resolved in this version. Tests provide baseline for verification across Java versions.

Original prompt

Add a new test case for WebSocketUpgradeSupport

There is an issue reported here https://bugs.java.com/bugdatabase/view_bug?bug_id=JDK-8361305

We should include this as a new testcase as it is releated to the HttpClient as well so we need to proof:

Directly connecting to a Websocketserver works when using

HttpClient client = HttpClient.newHttpClient();
WebSocket.Builder webSocketBuilder = client.newWebSocketBuilder();

on a ws:// URI, but it doe NOT work to UPGRADE

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