Salem is about to become a far more fashionable city thanks to a 90-year-old fashion icon who says she’ll bequeath a significant slice of her couture collection to the Peabody Essex Museum. Iris Apfel, the celebrated New York fashion doyenne best known for her saucer-sized glasses and chunky jewelry, will give the Peabody Essex more than 600 pieces of clothing and accessories by world-famous designers, a trove that she has amassed over more than five decades.