Core: Add StateMachine

Backported from legacy Nazara

include/Nazara/Core/State.hpp

@@ -0,0 +1,31 @@
+// Copyright (C) 2023 Jérôme "Lynix" Leclercq (lynix680@gmail.com)
+// This file is part of the "Nazara Engine - Core module"
+// For conditions of distribution and use, see copyright notice in Config.hpp
+
+#pragma once
+
+#ifndef NAZARA_CORE_STATE_HPP
+#define NAZARA_CORE_STATE_HPP
+
+#include <NazaraUtils/Prerequisites.hpp>
+#include <Nazara/Core/Config.hpp>
+#include <Nazara/Core/Time.hpp>
+
+namespace Nz
+{
+	class StateMachine;
+
+	class NAZARA_CORE_API State
+	{
+		public:
+			State() = default;
+			virtual ~State();
+
+			virtual void Enter(StateMachine& fsm) = 0;
+			virtual void Leave(StateMachine& fsm) = 0;
+
+			virtual bool Update(StateMachine& fsm, Time elapsedTime) = 0;
+	};
+}
+
+#endif // NAZARA_CORE_STATE_HPP