EVERY night, behind millions of closed eyelids, little New York movies flicker, as fleetingly as yesterday's fireworks: images of an Upper West Side apartment where one room opens into another, then another; of verdant midtown oases; of downtown lofts with streets running through them, of an A train that takes the dreamer far from Harlem. The imagination is well nourished in New York, which to many seems like a city that already has the mythical character of a dreamscape. In real life, elevators plunge into watery basements, office and apartment towers soar skyward and there is a feast of characters and symbols to feed on. Streets steam surreally, their surfaces sometimes cracking and opening into craters large enough to swallow a car or a human.