Two prominent billionaires hold large stakes in these growth stocks.Beating the market is a goal of every growth investor. There's no better place to look for stocks that can beat the market than prominent billionaire investors who have an interest in growing and protecting their wealth.Bill Ackman of Pershing Square Capital Management and former Microsoft CEO and co-founder Bill Gates are great sources to find promising investment ideas in the stock market. Let's look at two of their top holdings that can ...