Two sets of oil producers are fighting for dominance: the growing U.S. shale patch and the Organization of the Petroleum Exporting Countries. Investors are trying to figure out which side has the stronger hand. Oil prices are near 2019 highs, which could give the impression that OPEC, with its production cuts, is the current dominant force. But output from U.S. shale oil producers has doubled from its level five years ago, and more supply coming later in the year could flood markets yet again. …