The Hong Kong stock exchange greeted its busiest day in 18 months for new listings, with seven companies making their trading debuts, as the city enjoys a respite from social unrest in recent weeks.The number of listings is the most since eight companies began trading on July 12, 2018, according to exchange data. The raft of stock offerings in the new year underscores the confidence in Asia’s third largest capital market in the face of economic challenges brought on by months of anti-government…