LibJS: Only allow TimeZone this value in Temporal.TimeZone#toJSON

This is a normative change in the Temporal spec.

See: https://github.com/tc39/proposal-temporal/commit/2644fc6

Userland/Libraries/LibJS/Runtime/Temporal/TimeZonePrototype.cpp

@@ -230,10 +230,11 @@ JS_DEFINE_NATIVE_FUNCTION(TimeZonePrototype::to_string)
 JS_DEFINE_NATIVE_FUNCTION(TimeZonePrototype::to_json)
 {
     // 1. Let timeZone be the this value.
-    auto time_zone = vm.this_value(global_object);
+    // 2. Perform ? RequireInternalSlot(timeZone, [[InitializedTemporalTimeZone]]).
+    auto* time_zone = TRY(typed_this_object(global_object));
 
-    // 2. Return ? ToString(timeZone).
-    return js_string(vm, TRY(time_zone.to_string(global_object)));
+    // 3. Return ? ToString(timeZone).
+    return js_string(vm, TRY(Value(time_zone).to_string(global_object)));
 }
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/TimeZone/TimeZone.prototype.toJSON.js

@@ -7,8 +7,12 @@ describe("correct behavior", () => {
         const timeZone = new Temporal.TimeZone("UTC");
         expect(timeZone.toJSON()).toBe("UTC");
     });
+});
 
-    test("works with any this value", () => {
-        expect(Temporal.TimeZone.prototype.toJSON.call("foo")).toBe("foo");
+describe("errors", () => {
+    test("this value must be a Temporal.TimeZone object", () => {
+        expect(() => {
+            Temporal.TimeZone.prototype.toJSON.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.TimeZone");
     });
 });