Clio Barnard’s first feature-length documentary film, “The Arbor,” received The Douglas Hickox Award at the BIFAs, Best British Newcomer and the Sutherland Award at the BFI London Film Festival, Best New Documentary Filmmaker at Tribeca, and a BAFTA nomination for Outstanding Debut. Her second feature, “The Selfish Giant,” premiered as part of Cannes Director’s Fortnight…