Once regarded mostly as sources of money for professional money managers, sovereign funds have matured into aggressive investors. : LONDON — When Lucid Motors, an electric carmaker, announced that it had raised $1 billion in financing last month, the transaction appeared at first blush to be just another Silicon Valley megaround. But what made the deal stand out was the identity of the lead investor: the Public Investment Fund, or P.I.F., an arm of Saudi Arabia’s government charged with investing the kingdom’s oil fortune.