vfs: add vfs_cached for romfs build

src/core/file_sys/vfs_cached.h

@@ -0,0 +1,31 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <string_view>
+#include <vector>
+#include "core/file_sys/vfs.h"
+
+namespace FileSys {
+
+class CachedVfsDirectory : public ReadOnlyVfsDirectory {
+public:
+    CachedVfsDirectory(VirtualDir& source_directory);
+
+    ~CachedVfsDirectory() override;
+    VirtualFile GetFile(std::string_view file_name) const override;
+    VirtualDir GetSubdirectory(std::string_view dir_name) const override;
+    std::vector<VirtualFile> GetFiles() const override;
+    std::vector<VirtualDir> GetSubdirectories() const override;
+    std::string GetName() const override;
+    VirtualDir GetParentDirectory() const override;
+
+private:
+    std::string name;
+    VirtualDir parent;
+    std::map<std::string, VirtualDir, std::less<>> dirs;
+    std::map<std::string, VirtualFile, std::less<>> files;
+};
+
+} // namespace FileSys