Old zombie villagers cannot transition into all professions during the upgrading process

Before version 1.9, there was only one zombie villager skin. From version 1.9 to 1.13.2, there were six zombie villager skins. When upgrading worlds with zombie villagers from before version 1.14 or before 1.9, only certain professions can be applied to the zombie villagers, with the selection being random. This issue is related to MC-271565.

The following professions are possible to get:

• minecraft:armorer
• minecraft:butcher
• minecraft:cleric
• minecraft:farmer
• minecraft:librarian
• minecraft:nitwit (only when upgrading zombie villagers from 1.9 to 1.13.2)

The following professions are not possible to get when upgrading:

• minecraft:cartographer
• minecraft:fisherman
• minecraft:fletcher
• minecraft:leatherworker
• minecraft:nitwit (only when upgrading from before 1.9)
• minecraft:mason (didn't exist before 1.14, so they are only expected to be got when upgrading from before 1.9)
• minecraft:shepherd
• minecraft:toolsmith
• minecraft:weaponsmith

Each of the six skins from versions 1.9 to 1.13.2 can only correspond to one profession when upgrading.

Current behavior when upgrading from 1.9-1.13.2 to the latest version

• Zombie villagers from profession 0 only turn into farmers
• Zombie villagers from profession 1 only turn into librarians
• Zombie villagers from profession 2 always turn into clerics
• Zombie villagers from profession 3 only into armorers
• Zombie villagers from profession 4 only into butchers
• Zombie villagers from profession 5 always turn into nitwits

Expected behavior when upgrading from 1.9-1.13.2 to the latest version

• Zombie villagers from profession 0 should be able to turn into farmers, fletchers, fishermen and shepherds
• Zombie villagers from profession 1 should be able to turn into librarians and cartographers
• Zombie villagers from profession 2 should only be able to turn into clerics
• Zombie villagers from profession 3 should be able to turn into armorers, weaponsmiths and toolsmiths
• Zombie villagers from profession 4 should be able to turn into butchers and leatherworkers
• Zombie villagers from profession 5 should only be able to turn into nitwits

Current behavior when upgrading from before 1.9

• Zombie villagers can only transform into armorers, butchers, clerics, farmers, or librarians.

  Expected behavior when upgrading from before 1.9

• Zombie villagers ought to have the capability to transform into every available profession, encompassing cartographers, fishermen, fletchers, leatherworkers, nitwits, masons, shepherds, toolsmiths, and weaponsmiths.

Steps to reproduce (upgrading from before 1.9)

1. Start version 1.8.9
2. Summon a cluster of zombie villagers using the following command:

   /summon Zombie ~ ~ ~ {IsVillager:1b,PersistenceRequired:1b}

3. Upgrade the world to the latest version

4. /execute if entity @e[type=minecraft:zombie_villager,nbt={VillagerData:{profession:"minecraft:nitwit"}}]

5. Execute the command with all of the different professions

Steps to reproduce (upgrading from 1.9-1.13.2)

1. Start version 1.13.2
2. Spawn many zombie villagers
3. Upgrade the world to the latest version

4. /execute if entity @e[type=minecraft:zombie_villager,nbt={VillagerData:{profession:"minecraft:nitwit"}}]

5. Execute the command with all of the different professions