During a very grueling double raid right after 1.14 was released, when the pillagers were inside my base, and 6 ravagers were killing all the villagers, diamonds and emeralds and enchanted books appeared all over the place. I collected 100+ diamonds. I am not sure if this is a bug, or some raid mobs drop them when killed, or the villagers are wandering traders drop them when killed. The diamonds seemed to appear spontaneously on the ground spread over a large area.