LibJS: Implement Temporal.PlainDate.prototype.withCalendar

Author: https://github.com/IdanHo
Commit: 9fa8f19a0f
Pull-request: https://github.com/SerenityOS/serenity/pull/8961
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.withCalendar.js

@@ -0,0 +1,13 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.PlainDate.prototype.withCalendar).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = { hello: "friends" };
+        const firstPlainDate = new Temporal.PlainDate(1, 1, 1);
+        expect(firstPlainDate.calendar).not.toBe(calendar);
+        const secondPlainDate = firstPlainDate.withCalendar(calendar);
+        expect(secondPlainDate.calendar).toBe(calendar);
+    });
+});