By Steve Holland WASHINGTON (Reuters) -U.S. President Joe Biden pledged $800 million in more weaponry for Ukraine on Thursday and said he would ask Congress for more money to help bolster support for the Ukrainian military as it faces a fresh onslaught by Russia on its eastern flank. Addressing Americans from the White House’s Roosevelt Room, Biden pledged to send heavy artillery, dozens of howitzers, and 144,000 rounds of ammunition, as well as tactical drones, as he called on Congress for supplemental funding to provide additional aid for Kyiv. Biden also announced $500 million in direct eco…