WASHINGTON — Police across the United States are rethinking how they use force amid national outrage over questionable shootings and violent arrests.The changes include efforts in Dallas to train officers to de-escalate situations by moving backward during target practice and arming some with sponge projectiles rather than guns.In Camden, N.J., officers are taught about the sanctity of life and encouraged to take time to defuse a situation, even if a suspect is wildly waving a knife at them.After months of work, nearly 200 …