LibJS: Implement Temporal.ZonedDateTime.prototype.timeZone

Author: https://github.com/linusg
Commit: 49c5f87274
Pull-request: https://github.com/SerenityOS/serenity/pull/9160
Reviewed-by: https://github.com/IdanHo ✅

Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.timeZone.js

@@ -0,0 +1,15 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = new Temporal.ZonedDateTime(0n, timeZone);
+        expect(zonedDateTime.timeZone).toBe(timeZone);
+    });
+});
+
+test("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Reflect.get(Temporal.ZonedDateTime.prototype, "timeZone", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.ZonedDateTime");
+    });
+});