Tests: Add test for loading module scripts in Workers

Tests/LibWeb/Text/expected/Worker/Worker-module.txt

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+Message from worker: Worker responding to: Hello :^)

Tests/LibWeb/Text/input/Worker/Worker-module.html

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+<script src="../include.js"></script>
+<script>
+    asyncTest((done) => {
+        let work = new Worker('worker.mjs', { type: 'module' });
+        work.onmessage = (e) => {
+            println(`Message from worker: ${e.data}`);
+            work.onmessage = null;
+            work.terminate();
+            done();
+        };
+
+        work.onerror = (e) => {
+            println(`Worker error: ${e.message}`);
+        };
+
+        work.postMessage('Hello :^)');
+    });
+</script>

Tests/LibWeb/Text/input/Worker/worker.mjs

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+self.onmessage = ({ data }) => {
+    self.postMessage(`Worker responding to: ${data}`);
+};