Tesla Inc. is poised to begin its long-awaited robotaxi service in Austin on June 12, according to a person familiar with the matter, a milestone in Elon Musk’s plan to reshape the company around driverless vehicles and artificial intelligence.The previously unreported date was discussed internally and could still change, said the person, asking not to be identified because the information is private. Musk has previously said the service would begin by the end of June....