VideoCommon: add logic to read a GraphicsMod from configuration

Source/Core/VideoCommon/GraphicsModSystem/Config/GraphicsTarget.h

@@ -0,0 +1,56 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <optional>
+#include <string>
+#include <variant>
+
+#include <picojson.h>
+
+#include "Common/CommonTypes.h"
+#include "VideoCommon/TextureDecoder.h"
+#include "VideoCommon/XFMemory.h"
+
+struct TextureTarget
+{
+  std::string m_texture_info_string;
+};
+
+struct DrawStartedTextureTarget final : public TextureTarget
+{
+};
+
+struct LoadTextureTarget final : public TextureTarget
+{
+};
+
+struct FBTarget
+{
+  u32 m_height = 0;
+  u32 m_width = 0;
+  TextureFormat m_texture_format = TextureFormat::I4;
+};
+
+struct EFBTarget final : public FBTarget
+{
+};
+
+struct XFBTarget final : public FBTarget
+{
+};
+
+struct ProjectionTarget
+{
+  std::optional<std::string> m_texture_info_string;
+  ProjectionType m_projection_type = ProjectionType::Perspective;
+};
+
+using GraphicsTargetConfig = std::variant<DrawStartedTextureTarget, LoadTextureTarget, EFBTarget,
+                                          XFBTarget, ProjectionTarget>;
+
+std::optional<GraphicsTargetConfig> DeserializeTargetFromConfig(const picojson::object& obj);
+
+void SerializeTargetToProfile(picojson::object* obj, const GraphicsTargetConfig& target);
+void DeserializeTargetFromProfile(const picojson::object& obj, GraphicsTargetConfig* target);