Whether or not you’re a grandmother or live anywhere near a coast, you might be a coastal grandmother if your lifestyle aspirations involve things such as rumpled linen bedding, slipcovered sofas, blue-and-white interiors, dogeared Ina Garten recipe books, Nancy Meyers films like “Father of the Bride” and “The Holiday,” white button-downs, straw hats, and kitchen dance parties with your loved ones.