By Ted Hesson WASHINGTON (Reuters) -Tens of thousands of demonstrators descended on Washington and at hundreds of rallies across the United States on Saturday to demand that lawmakers pass legislation aimed at curbing gun violence following last month’s massacre at a Texas elementary school. In the nation’s capital, organizers with March for Our Lives (MFOL) estimated that 40,000 people assembled at the National Mall near the Washington Monument under occasional light rain. The gun safety group was founded by student survivors of the 2018 massacre at a Parkland, Florida, high school. Courtney …