Apple Inc. is planning a dedicated app for video games on its devices, seeking to sell gamers and developers on the idea that it’s a leader in the market.The company will preinstall the app on the iPhone, iPad, Mac and Apple TV set-top box later this year, according to people with knowledge of the matter. The software will serve as a launcher for titles and centralize in-game achievements, leaderboards, communications and other activity, said the people, who asked not to be identified because th...