Three times a week, millions of people who crave detailed explanations of time zones, deepfakes, artificial sweeteners and other trivia listen to the latest episodes of the podcast “Stuff You Should Know.” Soon, the program — already one of the most popular in the world, with more than a billion downloads over its 11 years — will have the chance to attract an even larger and more diverse audience, thanks to a global expansion planned by its new owner, the broadcast giant iHeartMedia.