''MAMMAME,'' which will be seen in its first New York screenings today and tomorrow at Film Forum 2, is the work of Raul Ruiz, the Chilean expatriate film director, and Jean-Claude Gallotta, the French experimentalist choreographer. Mr. Ruiz is a surrealist. Mr. Gallotta is a fabulist. And the surprisingly immediate private worlds of these two enfants terribles of the arts are ...