Allow enabling sand duping (#10191)

Because this exploit has been widely known for years and has not been fixed by Mojang, we decided that it was worth allowing people to toggle it on/off due to how easy it is to make it configurable.

It should be noted that this decision does not promise all future exploits will be configurable.

patches/server/0723-Fix-saving-in-unloadWorld.patch

@@ -0,0 +1,20 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Philip Kelley <philip@thoriumcube.org>
+Date: Wed, 16 Mar 2022 12:05:59 +0000
+Subject: [PATCH] Fix saving in unloadWorld
+
+Change savingDisabled to false to ensure ServerLevel's saving logic gets called when unloadWorld is called with save = true
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+index d8bec75e7f5c034051839818f51cdae71863608c..713d36b8bcb3f39f7f0cff61532199416970bcf4 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+@@ -1343,7 +1343,7 @@ public final class CraftServer implements Server {
+ 
+         try {
+             if (save) {
+-                handle.save(null, true, true);
++                handle.save(null, true, false); // Paper - Fix saving in unloadWorld
+             }
+ 
+             handle.getChunkSource().close(save);