Aided by a pack of cigarettes, a bottle of vodka, three actors and a pile of dead lemmings, Walt Disney will read you a screenplay he wrote about his final days on earth. This darkly imaginative, ambitiously titled, fiercely funny play by Lucas Hnath (Broadway’s A Doll’s House, Part 2;Hillary and Clinton) turns the public persona of the self-made American folk hero, creator of “The Happiest Place on Earth,” on its head — recounting, among other things, his failed attempt to make Disney World a functional working city and the urban legend of his cryogenically frozen head.