Emerging-market assets are so cheap that they may be “the trade of a decade,” according to Research Affiliates LLC, a sub-adviser to Pacific Investment Management Co., one of the world’s biggest money managers. They’re joining a growing number of investors, including BlackRock Inc., Franklin Templeton and Goldman Sachs Asset Management, who are turning bullish on emerging markets after three years of underperformance. With borrowing costs at the highest levels since the...