LibWeb: Add more document tests, add comment, text and mixin tests

Also adds a TypeScript definition file for the test runner object.

Libraries/LibWeb/Tests/DOM/mixins/NonElementParentNode.js

@@ -0,0 +1,19 @@
+loadPage("file:///home/anon/web-tests/Pages/ParentNode.html");
+
+afterInitialPageLoad(() => {
+    test("getElementById basics", () => {
+        const unique = document.getElementById("unique");
+        expect(unique).not.toBeNull();
+        expect(unique.nodeName).toBe("div");
+        expect(unique.id).toBe("unique");
+
+        const caseSensitive = document.getElementById("Unique");
+        expect(caseSensitive).toBeNull();
+
+        const firstDuplicate = document.getElementById("dupeId");
+        expect(firstDuplicate).not.toBeNull();
+        expect(firstDuplicate.nodeName).toBe("div");
+        expect(firstDuplicate.id).toBe("dupeId");
+        expect(firstDuplicate.innerHTML).toBe("First ID");
+    });
+});

Libraries/LibWeb/Tests/DOM/mixins/ParentNode.js

@@ -0,0 +1,25 @@
+loadPage("file:///home/anon/web-tests/Pages/ParentNode.html");
+
+afterInitialPageLoad(() => {
+    test("querySelector basics", () => {
+        const firstDuplicateElement = document.querySelector(".duplicate");
+        expect(firstDuplicateElement).not.toBeNull();
+        expect(firstDuplicateElement.nodeName).toBe("div");
+        expect(firstDuplicateElement.innerHTML).toBe("First");
+
+        const noElement = document.querySelector(".nonexistent");
+        expect(noElement).toBeNull();
+    });
+
+    test("querySelectorAll basics", () => {
+        const allDuplicates = document.querySelectorAll(".duplicate");
+        expect(allDuplicates).toHaveLength(2);
+        expect(allDuplicates[0].nodeName).toBe("div");
+        expect(allDuplicates[0].innerHTML).toBe("First");
+        expect(allDuplicates[1].nodeName).toBe("div");
+        expect(allDuplicates[1].innerHTML).toBe("Second");
+
+        const noElements = document.querySelectorAll(".nonexistent");
+        expect(noElements).toHaveLength(0);
+    });
+});