“Le Corbusier: An Atlas of Modern Landscapes,” newly installed at the Museum of Modern Art, is really two exhibitions. It’s on the one hand a sprawling introduction to the life and work of this Swiss-born giant, on a scale that MoMA, hard though it may be to believe, has never previously organized. A little pruning might have helped. Hypnotic videos sometimes get noisy, distractingly so. But as an omnibus, long overdue, the show is riveting, fun, a landmark.