There’s a bit of acting advice that’s often ascribed to Noël Coward: “Speak clearly, and don’t bump into the furniture.” But if you’re Kelli O’Hara and Rose Byrne , by all means, slide down the staircase, nosedive over the settee and slur your words while tossing back two strong martinis and a case of Dom Pérignon. The actors check every one of those boxes during the drunken high point of “ Fallen Angels ,” the revival of a nearly forgotten Coward play that’s being performed on Broadway for the