Kanye West never cut a duet with Orson Welles. But younger people should know him, and Chuck Workman’s fine, brisk and thoroughly entertaining overview of Orson, “Magician: The Astonishing Life and Work of Orson Welles,” easily makes the case why. In brilliant, light-handed strokes, Workman’s documentary captures the “boy genius,” the young tyro who was coddled through what could have been a traumatic childhood, indulged as he bluffed his way onto the stage and celebrated as he revolutionized the Depression Era theater, almost overnight, in his teens.