Common: Add utility function that wraps localtime_s() or localtime_t().

Source/Core/Common/TimeUtil.h

@@ -0,0 +1,13 @@
+// Copyright 2024 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <ctime>
+#include <optional>
+
+namespace Common
+{
+// Threadsafe and error-checking variant of std::localtime()
+std::optional<std::tm> Localtime(std::time_t time);
+}  // Namespace Common