The new exhibition at London’s Saatchi Gallery makes one thing clear: Contemporary art is now a truly global phenomenon. Once, Charles Saatchi used to go truffle hunting in the artist studios of London; now, he can find what he likes just about anywhere in the world. “Unveiled: New Art from the Middle East” (through May 6) is full of what you might call Saatchi-type art: brash, figurative, sometimes shocking. The mix is familiar. This is the kind of work he discovered in the London of the early 1990s and introduced to the public in the celebrated “Sensation” show of 1997. It was one of the triggers of the recent contemporary-art boom.