LibJS: Start implementing Temporal.ZonedDateTime

This commit adds the ZonedDateTime object itself, its constructor and
prototype (currently empty), and the CreateTemporalZonedDateTime
abstract operation.

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

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/Instant.h>
+#include <LibJS/Runtime/Temporal/ZonedDateTime.h>
+#include <LibJS/Runtime/Temporal/ZonedDateTimeConstructor.h>
+
+namespace JS::Temporal {
+
+// 6 Temporal.ZonedDateTime Objects, https://tc39.es/proposal-temporal/#sec-temporal-zoneddatetime-objects
+ZonedDateTime::ZonedDateTime(BigInt& nanoseconds, Object& time_zone, Object& calendar, Object& prototype)
+    : Object(prototype)
+    , m_nanoseconds(nanoseconds)
+    , m_time_zone(time_zone)
+    , m_calendar(calendar)
+{
+}
+
+void ZonedDateTime::visit_edges(Cell::Visitor& visitor)
+{
+    Base::visit_edges(visitor);
+
+    visitor.visit(&m_nanoseconds);
+    visitor.visit(&m_time_zone);
+    visitor.visit(&m_calendar);
+}
+
+// 6.5.3 CreateTemporalZonedDateTime ( epochNanoseconds, timeZone, calendar [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporalzoneddatetime
+ZonedDateTime* create_temporal_zoned_date_time(GlobalObject& global_object, BigInt& epoch_nanoseconds, Object& time_zone, Object& calendar, FunctionObject* new_target)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Assert: Type(epochNanoseconds) is BigInt.
+    // 3. Assert: Type(timeZone) is Object.
+    // 4. Assert: Type(calendar) is Object.
+
+    // 2. Assert: ! IsValidEpochNanoseconds(epochNanoseconds) is true.
+    VERIFY(is_valid_epoch_nanoseconds(epoch_nanoseconds));
+
+    // 5. If newTarget is not present, set it to %Temporal.ZonedDateTime%.
+    if (!new_target)
+        new_target = global_object.temporal_zoned_date_time_constructor();
+
+    // 6. Let object be ? OrdinaryCreateFromConstructor(newTarget, "%Temporal.ZonedDateTime.prototype%", « [[InitializedTemporalZonedDateTime]], [[Nanoseconds]], [[TimeZone]], [[Calendar]] »).
+    // 7. Set object.[[Nanoseconds]] to epochNanoseconds.
+    // 8. Set object.[[TimeZone]] to timeZone.
+    // 9. Set object.[[Calendar]] to calendar.
+    auto* object = ordinary_create_from_constructor<ZonedDateTime>(global_object, *new_target, &GlobalObject::temporal_time_zone_prototype, epoch_nanoseconds, time_zone, calendar);
+    if (vm.exception())
+        return {};
+
+    // 10. Return object.
+    return object;
+}
+
+}