The Royal Shakespeare Company has unveiled the full cast for its acclaimed production of “ Twelfth Night ,” directed by “The Crown” star Prasanna Puwanarajah, which transfers to London’s Barbican. Following a sold-out, five-star run in Stratford-upon-Avon that earned Puwanarajah the U.K. Theatre Award for best director, the show continues its life in the capital with a mix of returning cast members and fresh faces. Gwyneth Keyworth (“Death Valley,” “Misfits”) reprises her role as Viola,