It seemed like a simple assignment: Explain to readers what — or who — is Shen Yun. The short answer is, well, short. Shen Yun Performing Arts is the umbrella name for three companies of musicians, dancers, singers and acrobats reflecting “5,000 years of Chinese culture.” One company is based in New York, another in Europe and a third tours the U.S. Last year the show played the Music Hall. Thi…