“[The character Song Liling’s] true gender was the meant-to-shock big reveal of the original Broadway production … [But] by now, the play has been in the repertory for nearly 30 years. As [actor B.D.] Wong said by phone recently, ‘The cat is out of the bag.’ Yet here’s the thing, as I saw when I bought a ticket and went to an early preview: [David Henry] Hwang has made a new cat, and [Julie] Taymor has put it in a very different bag.” The playwright talks with Laura Collins-Hughes about that brand new bag.