Scores are not kept when a mob converts to another mob

When a mob transforms into another mob (ex. zombie villager → villager, mooshroom → cow), it loses all scores set with /scoreboard

Steps to reproduce:

1. Create a scoreboard 

   /scoreboard objectives add test dummy

2. Summon a villager
3. Give the villager a score 

   /scoreboard players add @e[type=minecraft:villager] test 1

4. Summon a zombie and let the villager be converted 

   /difficulty hard
   /time set midnight
   /summon minecraft:zombie

5. Get the scores of the new zombie villager 

   /scoreboard players list @e[type=minecraft:zombie_villager, sort=nearest, limit=1]

6. Expect the zombie villager to have the test score of 1 and be disappointed

Possibly related to MC-88967