LibJS: Add DisposableStack{, Prototype, Constructor}

Since the async parts of the spec are not stage 3 at this point we don't
add AsyncDisposableStack.

Userland/Libraries/LibJS/Tests/builtins/DisposableStack/DisposableStack.js

@@ -0,0 +1,18 @@
+test("constructor properties", () => {
+    expect(DisposableStack).toHaveLength(0);
+    expect(DisposableStack.name).toBe("DisposableStack");
+});
+
+describe("errors", () => {
+    test("called without new", () => {
+        expect(() => {
+            DisposableStack();
+        }).toThrowWithMessage(TypeError, "DisposableStack constructor must be called with 'new'");
+    });
+});
+
+describe("normal behavior", () => {
+    test("typeof", () => {
+        expect(typeof new DisposableStack()).toBe("object");
+    });
+});