SAN FRANCISCO — AI video-generation start-up Pika raised $80 million as venture capital investors continue to pour billions of dollars into artificial intelligence start-ups that are trying to compete with industry heavyweights OpenAI and Google.Pika joins other artificial intelligence video start-ups Runway and Synthesia in raising large amounts to build out their tools over the past year. Total venture capital investment in AI and machine-learning companies was $25.9 billion in the first quart...