Bring me a dream, Mr. Sandman. Make him the most adorable thing I’ve ever seen.” It’s 1958. Eisenhower is president, rock & roll is taking shape, and yet the Chordettes are stealing the spotlight with their sweet, unmistakable harmonies. Their a cappella hits “Mr. Sandman” and “Lollipop” made the quartet—Janet, Alice, Lynn, and Jinny—radio sensations…