[MC-126767] Spawn eggs no longer randomize spawned mob

Affects rabbits, villagers, zombie villagers, horses, llamas, parrots, sheep, zombies, skeletons, zombie pigmen, etc.

Mob types	Whether only spawn default variants	Whether the missing of weapons / armor / enchantment variants	Missing other variants
Villager	✔ brown	❌ not applicable	❌ not applicable
Rabbit	✔ brown	❌ not applicable	❌ not applicable
Sheep	✔ white	❌ not applicable	❌ not applicable
Horse	✔ white	❌ not applicable	❌ not applicable
Llama	✔ creamy	❌ not applicable	❌ not applicable
Parrot	✔ red	❌ not applicable	❌ not applicable
Slime	✔ Size:0	❌ not applicable	❌ not applicable
Magma cube	✔ Size:0	❌ not applicable	❌ not applicable
Zombie villager	✔ brown	✔	✔ baby, breaking doors, chicken jockeys, can pick up loot
Zombie	❌ not applicable	✔	✔ baby, breaking doors, chicken jockeys, can pick up loot
Zombie pigman	❌ not applicable	✔ default: golden sword	✔ baby, chicken jockeys, can pick up loot
Husk	❌ not applicable	✔	✔ baby, breaking doors, chicken jockeys, can pick up loot
Skeleton	❌ not applicable	✔ default: bow	✔ can pick up loot
Stray	❌ not applicable	✔ default: bow	✔ can pick up loot
Wither skeleton	❌ not applicable	✔ default: stone sword	✔ can pick up loot
Vex	❌ not applicable	✔ default: iron sword	❌ not applicable
Vindicator	❌ not applicable	✔ default: iron axe	✔ can pick up loot
Spider	❌ not applicable	❌ not applicable	✔ spawn with potion effects, spider jockeys