[desktop] Initial data manager prototype

Right now, all this adds is a small dialog to the Widgets frontend
showing the user how much space is taken up by their saves, shaders,
NAND, and mods. It also gives them the choice to clear these directories
(with 2x confirmation), OR open the directory in their system file
manager.

In the future, a lot more can be done with this concept. Notably, a
common import/export (a la android) could be added, the UI can obviously
be polished, etc. We could also add this to Android, but I don't think
common import/export is needed *for* Android, and should probably be
left in qt_common.

Signed-off-by: crueter <crueter@eden-emu.dev>

src/frontend_common/data_manager.h

@@ -0,0 +1,21 @@
+#ifndef DATA_MANAGER_H
+#define DATA_MANAGER_H
+
+#include "common/common_types.h"
+#include <string>
+
+namespace FrontendCommon::DataManager {
+
+enum class DataDir { Saves, UserNand, SysNand, Mods, Shaders };
+
+const std::string GetDataDir(DataDir dir);
+
+u64 ClearDir(DataDir dir);
+
+const std::string ReadableBytesSize(u64 size);
+
+u64 DataDirSize(DataDir dir);
+
+}; // namespace FrontendCommon::DataManager
+
+#endif // DATA_MANAGER_H