By Jeff Mason and Andrea Shalal WASHINGTON (Reuters) – Gun safety advocates are pushing U.S. President Joe Biden to take stronger measures on his own to curb gun violence after the Texas elementary school shooting, but the White House wants Congress to act first to have a more significant impact. The White House has spoken with gun safety groups since Tuesday’s rampage in Uvalde, Texas, in which 19 elementary school students and two teachers were killed – the deadliest school shooting in nearly a decade – activists said. The groups are urging Biden to make an emergency declaration on gun viole…