Move WidescreenHeuristic to it's own class

It's about the only thing left in renderer

Source/Core/VideoCommon/Widescreen.h

@@ -0,0 +1,34 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <memory>
+
+
+#include "VideoCommon/VideoConfig.h"
+#include "VideoCommon/VideoEvents.h"
+
+class PointerWrap;
+
+// This class is responsible for tracking the game's aspect ratio.
+class WidescreenManager
+{
+public:
+  WidescreenManager();
+
+  bool IsGameWidescreen() const { return m_is_game_widescreen; }
+
+  void DoState(PointerWrap& p);
+private:
+  void Update();
+  void UpdateWidescreenHeuristic();
+
+  bool m_is_game_widescreen = false;
+  bool m_was_orthographically_anamorphic = false;
+
+  EventHook m_update_widescreen;
+  EventHook m_config_changed;
+};
+
+extern std::unique_ptr<WidescreenManager> g_widescreen;