VideoBackends: Add Metal renderer

Source/Core/VideoBackends/Metal/VideoBackend.h

@@ -0,0 +1,27 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <string>
+#include "VideoCommon/VideoBackendBase.h"
+
+namespace Metal
+{
+class VideoBackend : public VideoBackendBase
+{
+public:
+  bool Initialize(const WindowSystemInfo& wsi) override;
+  void Shutdown() override;
+
+  std::string GetName() const override;
+  std::string GetDisplayName() const override;
+  std::optional<std::string> GetWarningMessage() const override;
+
+  void InitBackendInfo() override;
+
+  void PrepareWindow(WindowSystemInfo& wsi) override;
+
+  static constexpr const char* NAME = "Metal";
+};
+}  // namespace Metal