VideoBackends: Add Metal renderer

Source/Core/VideoBackends/Metal/MTLBoundingBox.h

@@ -0,0 +1,30 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "VideoCommon/BoundingBox.h"
+
+#include <Metal/Metal.h>
+
+#include "VideoBackends/Metal/MRCHelpers.h"
+
+namespace Metal
+{
+class BoundingBox final : public ::BoundingBox
+{
+public:
+  ~BoundingBox() override;
+
+  bool Initialize() override;
+
+protected:
+  std::vector<BBoxType> Read(u32 index, u32 length) override;
+  void Write(u32 index, const std::vector<BBoxType>& values) override;
+
+private:
+  BBoxType* m_cpu_buffer_ptr;
+  MRCOwned<id<MTLFence>> m_download_fence;
+  MRCOwned<id<MTLFence>> m_upload_fence;
+  MRCOwned<id<MTLBuffer>> m_cpu_buffer;
+  MRCOwned<id<MTLBuffer>> m_gpu_buffer;
+};
+}  // namespace Metal