Based on the 2018 Broadway musical and directed by unabashed showman Ryan Murphy, “The Prom” starts off strongly, with a kind of self-aware mockery of itself, as we are introduced to a quartet of washed-up NYC musical theater actors: Dee Dee, an aging legendary actress (Meryl Streep); Barry, a goofy sideman (James Corden); Trent, a pretentious Juilliard grad bartender (Andrew Rannells); and Angie, a 20-year “Chicago” chorus girl (Nicole Kidman).