Time for a quick lesson in regional fashion history, kids. From March 28 to June 27, our National Museum will showcase a historical collection of traditional Chinese dresses - cheongsams, including the ones worn by the Mmes of Wee Kim Wee, Benjamin Sheares, Ong Teng Cheong and Lee Kuan Yew. And before you go pooh-pooh at this old-skool form of dress, note that you'll see Vivienne Tam, John Galliano, and Alexander McQueen's takes on this iconic dress style.   The In The Mood for Cheongsam exhbition at the National Museum…