Hollywood's acting elite turned out en masse Thursday to watch Meryl Streep (of 19 West 12th Street) receive a lifetime achievement award from the American Film Institute. Among the heavyweights offering glowing testimonials at the Kodak Theater: Robert De Niro, Clint Eastwood, Jack Nicholson, Diane Keaton, Goldie Hawn, Shirley MacLaine and Jim Carrey.