LOS ANGELES (TheWrap.com) – The season finale of "The Voice" has enlisted some high-profile talent to help send the show's third cycle off with a bang. Rihanna, Kelly Clarkson, Bruno Mars and The Killers have been tapped to perform on the two-hour extravaganza, which will culminate with the crowning of a new champion, NBC said Wednesday. An additional special guest will be named at a later date, the network added. …