GameList: Add custom title/regions

Largely inspired by https://github.com/PCSX2/pcsx2/pull/9330, but almost
entirely rewritten.

src/duckstation-qt/mainwindow.h

@@ -107,6 +107,7 @@ public Q_SLOTS:
   void updateDebugMenuVisibility();
 
   void refreshGameList(bool invalidate_cache);
+  void refreshGameListModel();
   void cancelGameListRefresh();
 
   void runOnUIThread(const std::function<void()>& func);