In today's horror yarns, which are generally a cheap and creepy lot, there's a recent enthusiasm for ESP -- with a telepath, either good or evil, frequently being pursued by a government agent who wants to meddle with these mysterious powers. After "The Fury" and Stephen King's "Firestarter," we now have "Scanners," directed by David Cronenberg, the latest showmaker to develop a big reputation in the thriller field. Alas, "Scanners" doesn't hold up. The suspense is sporadic, the acting is uneven, the shocks are gruesome, and the logic would needm a mind reader to fill in the enormous gaps. Even when the hero links his psyche with a computer -- another budding SF trend -- the total IQ of this dopey movi e remains perilously close to zero.