Jem Aswad Senior Music EditorWhether or not you know Justin Tranter the person, if you’ve been near a radio in the past 10 years, you know Justin Tranter the songwriter, who’s had a hand in hits like Justin Bieber’s “Sorry,” DNCE’s “Cake by the Ocean,” Selena Gomez’s “Lose You to Love Me,” Imagine Dragons’ “Believer,” Halsey’s “Bad at Love” and dozens more.