Billie Eilish is levitating. Or so it seems. When the pop star first emerges on screen in the mouthful “Billie Eilish — Hit Me Hard and Soft: The Tour (Live in 3D),” she is suspended above a cube built of LED screens, surrounded by a sold-out crowd of over 23,000 fans in the center of the U.K.'s largest arena — Manchester 's Co-op Live. She launches into the midtempo “Chihiro,” a house experiment from her latest album, and the 3D magic begins. In the contemporary pop music landscape, Eilish is a rulebreaker — and so is this work. The new concert film, co-directed by Eilish and three-time Academy Award winner James Cameron , was his idea. Cameron emailed Eilish's mother, Maggie Baird — a friend of his wife via their shared interest in plant-based diets and environmentalism — and suggested they shoot Eilish's “Hit Me Hard and Soft” tour in 3D. It is new territory for Cameron, in some ways, and old hat in others.…