LibWeb: Implement <template> parsing

Note that there is currently no way to display them as we can't
currently clone nodes.

Adds special case for templates for dumping to console.
Doesn't add it to the DOM inspector as I'm not sure how to do it.

Libraries/LibWeb/Tests/HTML/HTMLTemplateElement.js

@@ -0,0 +1,27 @@
+loadPage("file:///home/anon/web-tests/Pages/Template.html");
+
+afterInitialPageLoad(() => {
+    test("Basic functionality", () => {
+        const template = document.getElementById("template");
+        expect(template).not.toBeNull();
+       
+        // The contents of a template element are not children of the actual element.
+        // The document fragment is not a child of the element either.
+        expect(template.firstChild).toBeNull();
+
+        // FIXME: Add this in once DocumentFragment's constructor is implemented.
+        //expect(template.content).toBeInstanceOf(DocumentFragment);
+        expect(template.content.nodeName).toBe("#document-fragment");
+
+        const templateDiv = template.content.getElementById("templatediv");
+        expect(templateDiv.nodeName).toBe("div");
+        expect(templateDiv.textContent).toBe("Hello template!");
+    });
+    
+    test("Templates are inert (e.g. scripts won't run)", () => {
+        // The page has a template element with a script element in it.
+        // Templates are inert, for example, they won't run scripts.
+        // That script will set "templateScriptRan" to true if it ran.
+        expect(window.templateScriptRan).toBeUndefined();
+    });
+});