LibJS: Start implementing Temporal.Duration

This patch adds the Duration object itself, its constructor and
prototype (currently empty), and three required abstract operations.

Userland/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.js

@@ -0,0 +1,35 @@
+describe("errors", () => {
+    test("called without new", () => {
+        expect(() => {
+            Temporal.Duration();
+        }).toThrowWithMessage(TypeError, "Temporal.Duration constructor must be called with 'new'");
+    });
+
+    test("cannot mix arguments with different signs", () => {
+        expect(() => {
+            new Temporal.Duration(-1, 1);
+        }).toThrowWithMessage(RangeError, "Invalid duration");
+        expect(() => {
+            new Temporal.Duration(1, -1);
+        }).toThrowWithMessage(RangeError, "Invalid duration");
+    });
+
+    test("cannot pass Infinity", () => {
+        expect(() => {
+            new Temporal.Duration(Infinity);
+        }).toThrowWithMessage(RangeError, "Invalid duration");
+    });
+});
+
+describe("normal behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.Duration).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const duration = new Temporal.Duration();
+        expect(typeof duration).toBe("object");
+        expect(duration).toBeInstanceOf(Temporal.Duration);
+        expect(Object.getPrototypeOf(duration)).toBe(Temporal.Duration.prototype);
+    });
+});