Numerous fixes to entity related changes

While it wasn't really "broken" before, if plugins use NMS
(which they really should't be) and mess with entity management
themselves, and get it wrong, they could ultimately corrupt our
state expectations.

I've been unable to reproduce any issues locally, but these changes
are the result of me analyzing the code pretty deeply and seeing
about how to make it more durable to abnormal usage.

Any servers seeing oddities, please run with -Ddebug.entities=true
and send me any logs triggered.

Spigot-Server-Patches/Optimize-Light-Recalculations.patch

@@ -7,7 +7,7 @@ Optimizes to not repeatedly look up the same chunk for
 light lookups.
 
 diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
-index fb00e7a9c..fabfc315c 100644
+index 4f64072a7b..966879a894 100644
 --- a/src/main/java/net/minecraft/server/Chunk.java
 +++ b/src/main/java/net/minecraft/server/Chunk.java
 @@ -0,0 +0,0 @@ public class Chunk implements IChunkAccess {
@@ -20,7 +20,7 @@ index fb00e7a9c..fabfc315c 100644
  
              this.x = true;
 diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
-index 739fbecac..739448d8b 100644
+index 97a0fbd55c..fb71879ac0 100644
 --- a/src/main/java/net/minecraft/server/World.java
 +++ b/src/main/java/net/minecraft/server/World.java
 @@ -0,0 +0,0 @@ public abstract class World implements IEntityAccess, GeneratorAccess, IIBlockAc