LibWeb: Add simple in-tree WebSocket test

Author: https://github.com/devgianlu
Commit: https://github.com/LadybirdBrowser/ladybird/commit/6889fa96957
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3571
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/alimpfard ✅

Tests/LibWeb/Text/expected/WebSocket/echo.txt

@@ -0,0 +1,7 @@
+open
+message WellHelloFriends0
+message WellHelloFriends1
+message WellHelloFriends2
+message WellHelloFriends3
+message WellHelloFriends4
+close

Tests/LibWeb/Text/input/WebSocket/echo.html

@@ -0,0 +1,35 @@
+<script src="../include.js"></script>
+<script>
+    asyncTest((done) => {
+        const ws = new WebSocket('wss://echo.websocket.org');
+
+        let messageCount = 0;
+
+        ws.onopen = function (ev) {
+            println(ev.type);
+
+            ws.onclose = function (ev) {
+                println(ev.type);
+                done();
+            }
+            ws.onerror = function (ev) {
+                println(ev.type);
+                done();
+            }
+        };
+        ws.onmessage = function (ev) {
+            if (ev.data.startsWith('WellHelloFriends')) {
+                println(`${ev.type} ${ev.data}`)
+            }
+
+            ws.send(`WellHelloFriends${messageCount}`);
+            if (messageCount++ === 5) {
+                ws.close();
+            }
+        }
+        ws.onerror = function (ev) {
+            println(ev.type);
+            done();
+        }
+    });
+</script>