GameList: Add status bar with game count

The status bar shows the number of games in your collection. If any
games are hidden by the platform, region, or search filters it will also
show how many games are visible and how many are filtered.

The visibility of the status bar can be toggled from the menu by
selecting `View`->`Show Game Count`.

Implements https://bugs.dolphin-emu.org/issues/9517.

Source/Core/DolphinQt/MainWindow.h

@@ -31,6 +31,7 @@ class CodeWidget;
 class DiscordHandler;
 class DragEnterEvent;
 class FreeLookWindow;
+class GameCount;
 class GameList;
 class GBATASInputWindow;
 class GCTASInputWindow;
@@ -241,6 +242,7 @@ private:
   MenuBar* m_menu_bar;
   SearchBar* m_search_bar;
   GameList* m_game_list;
+  GameCount* m_game_count;
   RenderWidget* m_render_widget = nullptr;
   bool m_rendering_to_main;
   bool m_stop_confirm_showing = false;