HONG KONG, Feb 27 Hong Kong’s stock exchange will bank on its role as a gateway to mainland China’s deep-pocketed investors to take on other leading venues and win the coveted $100 billion listing of Saudi Arabia’s giant state oil company, Aramco, it said on Monday. Charles Li, the CEO of Hong Kong Exchanges and Clearing , said access to Chinese capital and China’s role as the world’s largest importer of oil made Hong Kong a viable contender in the frantic race between listing venues.