Among the shiny, bouncy, madly infectious musical numbers that are a big part of what make Ryan Murphy’s “The Prom” such an old-fashioned newfangled blast, one of the show-stopping highlights is “Love Thy Neighbor,” which Trent (Andrew Rannells), a struggling Broadway drama queen who has landed on the distant planet known as small-town Indiana, sings to a bunch of clean-cut and pious Middle American teenagers from James Madison High School. They’re at a shopping-mall food court, where one of the students tells Trent, “We don’t have a drama program,” causing Trent to snap, “That explains your general lack of empathy.”