LibWeb: Create XML Documents in DOMParser.parseFromString

Author: https://github.com/shannonbooth
Commit: https://github.com/SerenityOS/serenity/commit/a545935997
Pull-request: https://github.com/SerenityOS/serenity/pull/22567
Reviewed-by: https://github.com/awesomekling

Tests/LibWeb/Text/input/DOM/DOMParser-xml-document.html

@@ -0,0 +1,8 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const parser = new DOMParser();
+        const xmlDoc = parser.parseFromString('<svg></svg>', "text/xml");
+        println(xmlDoc.constructor.name);
+    });
+</script>