It has been more than 20 years since the debut of Helgi Tomasson’s production of Tchaikovsky’s Swan Lake for the San Francisco Ballet. This time around the most-cherished and well-known of ballets gets a complete restaging featuring scenery and costumes by European designer Jonathan Fensom, who will try to avoid that “museum piece” feel. For this full-length premiere, one of the few this season, Tomasson says he was intruigued by working with Fensom, a newbie to ballet, but a Tony Award nominee (for Journey’s End in 2007) who has created costumes and sets for dozens of plays in London’s West End and on Broadway, plus some opera.