In my nearly half century of Broadway theatergoing, I've never witnessed such a second-act reversal of fortune as what's going on now at the Lunt-Fontanne Theatre, where 'Charlie and the Chocolate Factory' opened Sunday. Only in retrospective can you see glimmers of hope in the musical's desultory first half. Just one song by Marc Shaiman and Scott Wittman hits the mark in this retelling of Roald Dahl's tale of four children who win golden tickets to Willy Wonka's long-shuttered chocolate factory.