Flapping Airplanes, a year-old artificial intelligence startup, has raised $1 billion in funding at a $6 billion valuation — the latest example of investors betting on a newer crop of AI research labs that have yet to introduce commercial products. The financing, set to be announced Wednesday, was led by Index Ventures and Lux Capital. Other participants included Sequoia Capital, Alphabet Inc.’s GV and Kleiner Perkins. The company’s valuation, which includes the money raised, has quadrupled fro...