Playing a seven-inch Tinkerbell with pixie wings and pointy ears, Julia Roberts reminds the grown Peter Pan (Robin Williams) that the trick to flying is thinking happy thoughts. You get the feeling that the high-priced talents involved in Hook, including Dustin Hoffman in the villainous title role, are thinking profit participation. In updating Peter Pan for the Nineties, Steven Spielberg front-loads this $80 million epic with big stars, big sets and really big special effects (even Captain…