Simu Liu is revealing how he and his Barbie costars developed their Ken-ergy. To foster cast bonding for her big-screen adaptation of the iconic Mattel toys, writer-director Greta Gerwig gathered her actresses for a Barbie-themed sleepover. Liu, Ryan Gosling and the other actors playing Kens, however, had a different assignment. “Greta was very deliberate in what she wanted the Kens …