LibWeb: Add IDL definition for SVGScriptElement

It does not currently handle any of the actual scripting, but this
should at least allow us to create an instance of the element.

The test being added here isn't actually testing much, but before the
previous commit we used to crash parsing the page due to a TODO().

Tests/LibWeb/Text/input/SVG/svg-script-element.html

@@ -0,0 +1,7 @@
+<script src="../include.js"></script>
+<svg xmlns="http://www.w3.org/2000/svg"><script id="svg-script-element"></script></svg>
+<script>
+    test(() => {
+        println(`Name = ${document.getElementById('svg-script-element').constructor.name}`);
+    });
+</script>