Three stars. Rated PG. 126 minutes. “How Does a Moment Last Forever” is one of several new songs composed for Disney’s live-action adaptation of its animated classic, “Beauty and the Beast.” It’s also a subtle nod to the baggage that this production brings with it. How indeed to take a cartoon loved to the point of obsession, flesh it out with actors who can’t be expected to live up to the two-dimensional protagonists of fans’ imaginations, and open it up to lived-in realism, without losing the pure fantasy of the original?