CommonHostInterface: Add hotkeys for opening leaderboards/achievements

src/frontend-common/fullscreen_ui.h

@@ -49,6 +49,8 @@ void SystemDestroyed();
 void SystemPaused(bool paused);
 void OpenQuickMenu();
 void CloseQuickMenu();
+bool OpenAchievementsWindow();
+bool OpenLeaderboardsWindow();
 void Shutdown();
 void Render();