There’s a gleam in Nicolas Cage’s eye in “The Unbearable Weight of Massive Talent,” a welcome return for the Oscar winner who, for many years, seemed to be just going through the motions. For much of the 21st century, work has been just work for Cage, and in one sleepy project after another he seemed to show up, do his dance, collect a paycheck and leave. There were glimmers of hope — “Joe,” “Mandy,” last year’s “Pig” — but they almost seemed like accidents; even a broken clock, you know the rest. But in “Massive Talent,” the massive talent is back. And Nicolas Cage is, once again, ready to ro…