It makes perfect sense that his autobiography is onstage. And no less a modern theater icon than James Lapine has adapted and directed the play, using the stage thrillingly in a way the book could not. The sweet 'Act One,' which opened Thursday at the Vivian Beaumont Theater, faithfully and chronologically charts Hart's rise from poverty in the Bronx to co-writing with Kaufman 'Once In a Lifetime' in 1930, his first Broadway hit. But it's of course more than that: The majority of the 22 actors play multiple parts, jumping in and out of characters and costumes while the bold, complex set by Beowulf Boritt spins and spins. So in its very fiber and execution, it's a celebration of the theater itself.