By Diego Oré and Alvaro Murillo SAN JOSE (Reuters) -Anti-establishment economist Rodrigo Chaves clinched Costa Rica’s presidency on Sunday, upending decades of political consensus in the Central American country that is grappling with growing social discontent and mounting national debt. Chaves, a veteran former official of the World Bank, was projected to win about 52.9% of the vote in the run-off ballot, a preliminary tally by the electoral tribunal showed, based on returns from some 97% of polling stations. Rival candidate and former Costa Rican president Jose Maria Figueres was seen securi…