This enables us a fast reference to the entities current chunk instead
of having to look it up by hashmap lookups.
We also store counts by type to further enable other performance optimizations in later patches.
This fixes a CRITICAL missing part of the Bukkit API due to mistakes on upstream
refusing to implement the Sentient NPC baseclass of all NPC's.
Until now, the Bukkit API has not provided a way for accessing and setting
a non creature entities target.
Although Flying, Slime, Ambient, and Water mobs all supported targets internally,
you were unable to get/set it.
Now with the SentientNPC API and these API's moved down, every sentient NPC has
access to target data.
Aikar