Hong Kong is planning a big party as it marks 20 years under Chinese rule. But many people in the former British colony are not in the mood to celebrate.Fireworks, a gala variety show and Chinese military displays are among the official events planned to coincide with a visit by Chinese President Xi Jinping starting Thursday for the occasion. Ahead of the anniversary, state broadcaster China Central Television has been running daily news features extolling what it calls the inextricable ties between China and Hong Kong in fields ranging from sports to the military and the arts. Underneath the surface, however, tensions are simmering as Hong Kongers, especially the young, chafe at life under the tightening grip of China’s Communist leaders.