Enforce Sync Chunk Unloads

Unloading Chunks async is extremely dangerous. This will force it to main
the same way we handle async chunk loads.

Spigot-API-Patches/0048-Provide-E-TE-Chunk-count-stat-methods.patch

@@ -1,4 +1,4 @@
-From 604dc8e444593ab84281c94ca4eb334164c96ea8 Mon Sep 17 00:00:00 2001
+From 20f93fadc1651fc03cbd926370d79d191a3fe1f1 Mon Sep 17 00:00:00 2001
 From: Aikar <aikar@aikar.co>
 Date: Sat, 7 Jan 2017 15:23:03 -0500
 Subject: [PATCH] Provide E/TE/Chunk count stat methods
@@ -7,17 +7,32 @@ Provides counts without the ineffeciency of using .getEntities().size()
 which creates copy of the collections.
 
 diff --git a/src/main/java/org/bukkit/World.java b/src/main/java/org/bukkit/World.java
-index 56f50296..63cdcdb8 100644
+index 56f50296..2b6136fd 100644
 --- a/src/main/java/org/bukkit/World.java
 +++ b/src/main/java/org/bukkit/World.java
-@@ -24,6 +24,13 @@ import org.bukkit.util.Vector;
+@@ -24,6 +24,28 @@ import org.bukkit.util.Vector;
   */
  public interface World extends PluginMessageRecipient, Metadatable {
  
 +    // Paper start
++    /**
++     * @return The amount of Entities in this world
++     */
 +    int getEntityCount();
++
++    /**
++     * @return The amount of Tile Entities in this world
++     */
 +    int getTileEntityCount();
++
++    /**
++     * @return The amount of Tickable Tile Entities in this world
++     */
 +    int getTickableTileEntityCount();
++
++    /**
++     * @return The amount of Chunks in this world
++     */
 +    int getChunkCount();
 +    // Paper end
 +