SHANGHAI — Protesters angered by strict anti-virus measures called for China’s powerful leader to resign, an unprecedented rebuke as authorities in at least eight cities struggled to suppress demonstrations Sunday that represent a rare direct challenge to the ruling Communist Party.Police using pepper spray drove away demonstrators in Shanghai who called for Xi Jinping to step down and an end to one-party rule, but hours later, people rallied again in the same spot. Police again broke up the demonstration, and a reporter saw protesters under arrest being driven away in a bus.The protests — which began Friday and have spread...