GameList: Add custom title/regions

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

src/duckstation-qt/gamelistwidget.h

@@ -45,6 +45,7 @@ public:
   void resizeTableViewColumnsToFit();
 
   void refresh(bool invalidate_cache);
+  void refreshModel();
   void cancelRefresh();
   void reloadThemeSpecificImages();