By Steve Holland and Jeff Mason WASHINGTON (Reuters) -President Joe Biden will deliver a rare primetime address on tackling gun violence on Thursday evening after a string of mass shootings led to renewed calls for action on gun safety in the United States. The president will speak at 7:30 pm (2330 GMT) from the White House. His speech follows high-profile mass shootings in recent weeks at a grocery story in New York, an elementary school in Texas and a medical building in Oklahoma. Gun safety advocates are pushing Biden to take stronger measures on his own to curb gun violence, but the White …