His performances in “Spring Awakening” and “American Idiot” are probably what John Gallagher Jr. is most known for at the moment (he won a Tony for the former), and are often what get him labeled a “musical theater guy,” but they were the only musicals he’s done in his nearly 20 year career. I ask him about two recent play productions (“Long Day’s Journey Into Night” and “Jerusalem”) that I suspect were very formative for him, and his latest screen role in the important and moving indie “The Miseducation of Cameron Post.” And, of course, I couldn’t let him go without talking about Sorkin.