Persistent hostile mobs should persist when switched to Peaceful

Mostly intended for name tagged hostile mobs, but also useful for zombies holding dropped items and hostile mobs manually summoned with commands to have the persistent tag. Currently, if the difficulty of the game is accidentally set to peaceful (easily done from the menu), any loaded hostile mobs will disappear instantly regardless of whether they have a persistent tag. side effects of accidental switching may include: - loss of nametagged hostile mob pets - broken farms - loss of items currently held or worn by the mob (tested that one on bedrock but not java, results may vary) With the proposed change: any hostile mobs with a persistent tag would remain after switching to peaceful, such as those which are nametagged, holding an item or manually summoned with persistence. And if the switch to peaceful was intentional, worst case is having to manually clean up the remaining hostile mobs (with peaceful regeneration) But in the best case, it would allow players to place specific persistent hostile mobs they want in the world, then set the world to peaceful so no others will spawn.