Use distance map to optimise entity tracker / Misc Utils

Use the distance map to find candidate players for tracking.

This also ports a few utility changes from Tuinity

Spigot-Server-Patches/incremental-chunk-saving.patch

@@ -29,7 +29,7 @@ index 071e5e7f72..4867615215 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
-index 7bcdbe713d..4b77934c39 100644
+index 165cb994e8..af0d6aff4d 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 {
@@ -175,7 +175,7 @@ index a640cb3845..3d255b1964 100644
      public void a(ProtoChunkExtension protochunkextension) {
          for (int i = 0; i < this.statusFutures.length(); ++i) {
 diff --git a/src/main/java/net/minecraft/server/PlayerChunkMap.java b/src/main/java/net/minecraft/server/PlayerChunkMap.java
-index 6122d19ccf..4682dca9de 100644
+index 34f470779f..4f5b516144 100644
 --- a/src/main/java/net/minecraft/server/PlayerChunkMap.java
 +++ b/src/main/java/net/minecraft/server/PlayerChunkMap.java
 @@ -0,0 +0,0 @@ public class PlayerChunkMap extends IChunkLoader implements PlayerChunk.d {
@@ -261,7 +261,7 @@ index 6122d19ccf..4682dca9de 100644
                      return PlayerChunk.getChunkState(playerchunk.getTicketLevel());
                  });
 diff --git a/src/main/java/net/minecraft/server/WorldServer.java b/src/main/java/net/minecraft/server/WorldServer.java
-index 389c9d03a1..62c2275098 100644
+index ce506e0e12..ad5e538b24 100644
 --- a/src/main/java/net/minecraft/server/WorldServer.java
 +++ b/src/main/java/net/minecraft/server/WorldServer.java
 @@ -0,0 +0,0 @@ public class WorldServer extends World {