By DAVID LITTLEJOHN San Francisco As the opening of what the producers hope will be a 20-month-long U.S. run--beginning with a stay of several months here--a visually dazzling, London-born production of J.M. Barrie's "Peter Pan" opened in May in a round white tent, erected in the big public plaza across The Embarcadero from San Francisco's welcoming Ferry Building of 1898.