If, like me, you liked the NBC series Smash, a fictional musical drama about the making of a Broadway musical about Marilyn Monroe, you’ll love this. The musical within the musical, eventually titled “Bombshell,” was supposed to be fictional too. But by the time Smash was over, enough songs had been written, and production numbers staged, for “Bombshell” to look like a tantalizing prospect for the actual stage. And that actually happened, once, w