In a unique staging by the Royal Opera, Francesco Cavalli’s L’Ormindo is to be performed in a London theatre built to evoke the period when the piece was writtenThe Baroque music world is obsessed with playing on ‘original instruments’,” says Kasper Holten, the Royal Opera’s ­director whose staging of a 1644 opera is about to open at the newly opened Sam Wanamaker Playhouse next door to the Globe Theatre on London’s Bankside. “Well, this theatre is the most ‘original instrument’ imaginable.” It’s a first for opera: a number of cute ­eighteenth-century theatres around the world have staged the works of Mozart and his contemporaries, but operas from the art form’s infancy have never been seen in the kind o