Facing a future with less water, the country’s largest agricultural water district is turning from growing nuts, vegetables, fruit and beef to a new crop: solar power. Westlands Water District, which supplies some of California’s driest farmland in the Central Valley, is making plans to convert some 200 square miles of it — an area roughly the size of Detroit — into what would be the largest solar installation in the world. The move marks both an economic and political diversification for a district usually better known for its ties to former President Donald Trump and for fighting aggressively for every extra drop of water it can get.