Meta Platforms Inc. has finalized a multibillion-dollar investment in Scale AI and recruited the startup’s chief executive officer to join its artificial intelligence efforts — an unusual deal that signals a heightened push by the social media giant to catch up on AI development. Meta said Thursday that it has backed Scale, without including details. The size of the investment was $14.3 billion, according to a person familiar with the matter. The deal values the startup at more than $29 billion,...