Brian Eno has taken many musical forms: producer, technologist, glam-rock star. Eno, the new documentary about the musician, also takes many forms, though more literally. Each showing of the movie, which opens today in New York at Film Forum, will be a different version. It is, according to its makers, “the first generative feature film,” meaning pieces of it will change shape and structure per viewing, thanks to some clever software ingenuity designed by director Gary Hustwit and his partner Br...