LibJS: Start implementing Temporal.Calendar

Just like the previous Temporal.{Instant,TimeZone} commits, this patch
adds the Calendar object itself, its constructor and prototype
(currently empty), and two required abstract operations.

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

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/Calendar.h>
+#include <LibJS/Runtime/Temporal/CalendarConstructor.h>
+
+namespace JS::Temporal {
+
+// 12.2 The Temporal.Calendar Constructor, https://tc39.es/proposal-temporal/#sec-temporal-calendar-constructor
+CalendarConstructor::CalendarConstructor(GlobalObject& global_object)
+    : NativeFunction(vm().names.Calendar.as_string(), *global_object.function_prototype())
+{
+}
+
+void CalendarConstructor::initialize(GlobalObject& global_object)
+{
+    NativeFunction::initialize(global_object);
+
+    auto& vm = this->vm();
+
+    // 12.3.1 Temporal.Calendar.prototype, https://tc39.es/proposal-temporal/#sec-temporal-calendar-prototype
+    define_direct_property(vm.names.prototype, global_object.temporal_calendar_prototype(), 0);
+
+    define_direct_property(vm.names.length, Value(1), Attribute::Configurable);
+}
+
+// 12.2.1 Temporal.Calendar ( id ), https://tc39.es/proposal-temporal/#sec-temporal.calendar
+Value CalendarConstructor::call()
+{
+    auto& vm = this->vm();
+
+    // 1. If NewTarget is undefined, then
+    // a. Throw a TypeError exception.
+    vm.throw_exception<TypeError>(global_object(), ErrorType::ConstructorWithoutNew, "Temporal.Calendar");
+    return {};
+}
+
+// 12.2.1 Temporal.Calendar ( id ), https://tc39.es/proposal-temporal/#sec-temporal.calendar
+Value CalendarConstructor::construct(FunctionObject& new_target)
+{
+    auto& vm = this->vm();
+    auto& global_object = this->global_object();
+
+    // 2. Set id to ? ToString(id).
+    auto identifier = vm.argument(0).to_string(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. If ! IsBuiltinCalendar(id) is false, then
+    if (!is_builtin_calendar(identifier)) {
+        // a. Throw a RangeError exception.
+        vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidCalendarIdentifier, identifier);
+        return {};
+    }
+
+    // 4. Return ? CreateTemporalCalendar(id, NewTarget).
+    return create_temporal_calendar(global_object, identifier, &new_target);
+}
+
+}