Alexandre Moors (Blue Caprice) returns to Sundance this year with The Yellow Birds, based on the Kevin Powers novel about young soldiers at war, the effect it has on them when they return home, and the questions they face when one of their number doesn’t return. Alden Ehrenreich plays Brandon Bartle, tasked by his Staff Sergeant (Jack Huston) to look after Murph (Tye Sheridan), who is far from ready for the traumas of the front lines. Ehrenreich couldn’t make it to the…