Regardless of how Bank of America shareholders vote today on splitting the position of chairman and CEO, the proposal already is a bruising chapter for BofA Chairman and CEO Brian Moynihan and the bank's relationship with investors. BofA set the stage for a showdown with some of the world's largest investors, creating a venue for investors to voice concerns over issues involving shareholder activism and corporate governance. Today's vote is widely expected to be close, with major investors and…