Add files from mc-dev for diff visibility.
[Bleeding] Add many missing SpawnReasons.

Adds BUKKIT-5370, BUKKIT-5377, BUKKIT-5378, BUKKIT-5379, BUKKIT-5380,
BUKKIT-5381, BUKKIT-5382. Adds reasons for zombies infecting villagers and
zombie villagers being cured. Readds reason for a skeleton being spawned as
a spider jockey. Adds reason to distinguish ocelot babies from the parent
they spawned with. Adds reasons for chunk generation causing the ender
dragon, villagers, and witches to spawn. And finally, adds a reason for
spawning a chicken mount for a baby zombie.