Common: Add class 'FilesystemWatcher' that is used to watch paths and receive callbacks about filesystem level events for anything under that path

Source/Core/Common/FilesystemWatcher.h

@@ -0,0 +1,47 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <map>
+#include <memory>
+#include <string>
+#include <string_view>
+
+namespace wtr
+{
+inline namespace watcher
+{
+class watch;
+}
+}  // namespace wtr
+
+namespace Common
+{
+// A class that can watch a path and receive callbacks
+// when files or directories underneath that path receive events
+class FilesystemWatcher
+{
+public:
+  FilesystemWatcher();
+  virtual ~FilesystemWatcher();
+
+  void Watch(const std::string& path);
+  void Unwatch(const std::string& path);
+
+private:
+  // A new file or folder was added to one of the watched paths
+  virtual void PathAdded(std::string_view path) {}
+
+  // A file or folder was modified in one of the watched paths
+  virtual void PathModified(std::string_view path) {}
+
+  // A file or folder was renamed in one of the watched paths
+  virtual void PathRenamed(std::string_view old_path, std::string_view new_path) {}
+
+  // A file or folder was deleted in one of the watched paths
+  virtual void PathDeleted(std::string_view path) {}
+
+  std::map<std::string, std::unique_ptr<wtr::watch>> m_watched_paths;
+};
+}  // namespace Common