LONDON — A police officer shot and killed a man wearing a fake bomb on London Bridge on Friday, after several people were stabbed in what the police called a terrorist incident, which paralyzed one of the busiest arteries through the city. The chaotic clash, in a country where shootings are rare, involved several officers and civilians, and sent scores of people fleeing from the bridge and areas near it on both sides of the River Thames. It also revived memories of recent terrorist attacks in London, including one on the same bridge in 2017 that killed eight people. “It...