VideoBackends / VideoCommon: add support for specifying include files in shader code

Source/Core/VideoCommon/ShaderCompileUtils.h

@@ -0,0 +1,46 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "ShaderLang.h"
+
+namespace VideoCommon
+{
+class ShaderIncluder final : public glslang::TShader::Includer
+{
+public:
+  ShaderIncluder(const std::string& user_path, const std::string& system_path);
+  ~ShaderIncluder() override = default;
+
+  std::vector<std::string> GetIncludes() const;
+
+private:
+  IncludeResult* includeLocal(const char* header_name, const char* includer_name,
+                              std::size_t depth) override;
+  IncludeResult* includeSystem(const char* header_name, const char* includer_name,
+                               std::size_t depth) override;
+  void releaseInclude(IncludeResult* result) override;
+
+  IncludeResult* ProcessInclude(const std::string& root, const char* header_name,
+                                const char* includer_name, std::size_t depth);
+  std::string_view GetDirectory(std::string_view path) const;
+
+  std::string m_root_user_path;
+  std::string m_root_system_path;
+  std::vector<std::string> m_dirs;
+
+  struct IncludeResultData
+  {
+    std::unique_ptr<IncludeResult> result;
+    std::string file_data;
+  };
+  std::map<std::string, IncludeResultData, std::less<>> m_include_results;
+};
+
+}  // namespace VideoCommon