LibJS: Start implementing Temporal.TimeZone

Here we got our first Temporal object :^)
This patch adds the TimeZone object itself, its constructor and
prototype (currently empty), and a bunch of required abstract operations

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

@@ -0,0 +1,95 @@
+/*
+ * 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/ISO8601.h>
+#include <LibJS/Runtime/Temporal/TimeZone.h>
+#include <LibJS/Runtime/Temporal/TimeZoneConstructor.h>
+
+namespace JS::Temporal {
+
+// 11 Temporal.TimeZone Objects, https://tc39.es/proposal-temporal/#sec-temporal-timezone-objects
+TimeZone::TimeZone(String identifier, Object& prototype)
+    : Object(prototype)
+    , m_identifier(move(identifier))
+{
+}
+
+// 11.1.1 IsValidTimeZoneName ( timeZone ), https://tc39.es/proposal-temporal/#sec-isvalidtimezonename
+// NOTE: This is the minimum implementation of IsValidTimeZoneName, supporting only the "UTC" time zone.
+bool is_valid_time_zone_name(String const& time_zone)
+{
+    // 1. Assert: Type(timeZone) is String.
+
+    // 2. Let tzText be ! StringToCodePoints(timeZone).
+    // 3. Let tzUpperText be the result of toUppercase(tzText), according to the Unicode Default Case Conversion algorithm.
+    // 4. Let tzUpper be ! CodePointsToString(tzUpperText).
+    auto tz_upper = time_zone.to_uppercase();
+
+    // 5. If tzUpper and "UTC" are the same sequence of code points, return true.
+    if (tz_upper == "UTC")
+        return true;
+
+    // 6. Return false.
+    return false;
+}
+
+// 11.1.2 CanonicalizeTimeZoneName ( timeZone ), https://tc39.es/proposal-temporal/#sec-canonicalizetimezonename
+// NOTE: This is the minimum implementation of CanonicalizeTimeZoneName, supporting only the "UTC" time zone.
+String canonicalize_time_zone_name(String const& time_zone)
+{
+    // 1. Assert: Type(timeZone) is String.
+
+    // 2. Assert: ! IsValidTimeZoneName(timeZone) is true.
+    VERIFY(is_valid_time_zone_name(time_zone));
+
+    // 3. Return "UTC".
+    return "UTC";
+}
+
+// 11.1.3 DefaultTimeZone ( ), https://tc39.es/proposal-temporal/#sec-defaulttimezone
+// NOTE: This is the minimum implementation of DefaultTimeZone, supporting only the "UTC" time zone.
+String default_time_zone()
+{
+    // 1. Return "UTC".
+    return "UTC";
+}
+
+// 11.6.2 CreateTemporalTimeZone ( identifier [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporaltimezone
+Object* create_temporal_time_zone(GlobalObject& global_object, String const& identifier, FunctionObject* new_target)
+{
+    auto& vm = global_object.vm();
+
+    // 1. If newTarget is not present, set it to %Temporal.TimeZone%.
+    if (!new_target)
+        new_target = global_object.temporal_time_zone_constructor();
+
+    // 2. Let object be ? OrdinaryCreateFromConstructor(newTarget, "%Temporal.TimeZone.prototype%", « [[InitializedTemporalTimeZone]], [[Identifier]], [[OffsetNanoseconds]] »).
+    // 3. Set object.[[Identifier]] to identifier.
+    auto* object = ordinary_create_from_constructor<TimeZone>(global_object, *new_target, &GlobalObject::temporal_time_zone_prototype, identifier);
+    if (vm.exception())
+        return {};
+
+    // 4. If identifier satisfies the syntax of a TimeZoneNumericUTCOffset (see 13.33), then
+    if (is_valid_time_zone_numeric_utc_offset(identifier)) {
+        // TODO:
+        // a. Set object.[[OffsetNanoseconds]] to ! ParseTimeZoneOffsetString(identifier).
+    }
+    // 5. Else,
+    else {
+        // a. Assert: ! CanonicalizeTimeZoneName(identifier) is identifier.
+        VERIFY(canonicalize_time_zone_name(identifier) == identifier);
+
+        // b. Set object.[[OffsetNanoseconds]] to undefined.
+        // NOTE: No-op.
+    }
+
+    // 6. Return object.
+    return object;
+}
+
+}