Last season, “Hamilton” was the 800-pound gorilla in Orange County’s theater line-up. This year, that larger-than-life primate would be “Dear Evan Hansen,” a musical about a high school student with severe social anxiety. Like “Hamilton,” it sounds unpromising on paper, but it took Broadway by storm last year, winning six Tony Awards, including best musical and best score, and it’s hugely popular with – you guessed it – high school students. “Dear Evan Hansen” moves into Segerstrom Center for the Arts on Jan. 1 and stays for 13 days.