Description: When a named Villager (with a Name Tag) is converted into a Zombie, it loses its PersistenceRequired value, causing it to despawn if the player is far enough.

Steps to reproduce: For ease, you can reproduce it in Creative, but it happens in Survival too.

1. Spawn a Villager
2. Give it a name using a Name Tag
3. Use /data get entity <entity id> PersistenceRequired (to confirm that it switched to 1b)
4. Get it converted by zombies
5. Use /data get entity <entity id> PersistenceRequired again (the data tag is now 0b)
6. /tp <Player> ~ ~150 ~
7. /tp <Player> ~ ~-150 ~

The Villager has despawned.