Here’s the kind of entertainment you’d be hard-pressed to find in a modern movie or TV show. It’s a scene from Andrew Stone’s “Stormy Weather” (1943). The movie starred Lena Horne and Bill “Bojangles” Robinson, although neither of them are in this scene, which takes place in a nightclub where Cab Calloway is performing “Jumpin’ Jive” with his big band. At one point he strolls over to a corner of the audience where the Nicholas Brothers (Harold and Fayard) pop up from their chairs and completely take over. What follows is what many — including no less an expert than Fred Astaire — consider the greatest dance routine ever captured on film…