The former hedge fund of one of the Democratic Party’s most important donors was involved in a scheme to defraud foreign investors out of tens of millions of dollars, according to documents filed in a Texas court. Farallon Capital Partners L.P., a fund run by Farallon Capital Management, the multibillion-dollar hedge fund founded by Democratic donor Tom Steyer, became a limited partner in a project to build a large shopping mall near Seattle, Wash., in the mid-1990s after it guaranteed a line of credit for the project.