A bashful 11-year-old named Crystal had a question for Zara Larsson: “How did you become the perfect star?”Onstage, the singer — Barbie-like in a neon-pink tube top and flowing blond extensions — giggled into her bedazzled mic while a small group of VIP fans awwed. They had assembled in the cavernous, gilded hall of the Brooklyn Paramount for an “intimate pre-show hang” with Larsson, where she dutifully performed two acoustic songs and took questions.Later that March evening, a swarm of tweens, teens and gay millennials in glitter descended on the theatre for the second of Larsson’s two concerts there, during…