NEW YORK — After Madonna’s corsets and the vintage slip trend of the Nineties, the concept of underwear as ready-to-wear doesn’t shock as it once did. And that’s a good thing. So, in a season of pretty lace and frills, it’s only natural that designers are celebrating lingerie shapes. Here, from a house that has made the look its own, D&G’s silk slipdress and linen corset. Necklace by Gioia. For more, see pages 4 and 5.