Just over a decade ago, no one in America would have dared mount a festival of music by Soviet composers who were compelled to write inane Socialist Realist glorifications of Josef Stalin and the Party. The backlash would have been tremendous. Now, with the Soviet Union more than ten years dead, its history is more easily examined without the bluster of American righteousness, and Vladimir Ashkenazy is seizing the moment. Ashkenazy is at Carnegie Hall this week, mounting a festival of music dedicated to works composed under duress by Soviet composers.