Fans came out in droves to see Warner Bros.' DC Entertainment flick Shazam! this weekend, but as comics fans around the world know, Billy Batson's superhero story is only part of the legend. Zachary Levi/Asher Angel are now the faces of the two sides of the title hero, and they've got a long franchise road ahead of them if the origin movie's success is any indication, but another more powerful entity lurks on the horizon. That supervillain/antihero is Black Adam and Hollywood superstar Dwayne "The Rock" Johnson is set to bring him to life on …