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/0927-Implement-OfflinePlayer-isConnected.patch

@@ -0,0 +1,42 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aeltumn <daniel@goossens.ch>
+Date: Thu, 24 Aug 2023 13:05:30 +0200
+Subject: [PATCH] Implement OfflinePlayer#isConnected
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftOfflinePlayer.java b/src/main/java/org/bukkit/craftbukkit/CraftOfflinePlayer.java
+index 96408d505ce80799868ff84554a3b0b25adabb22..4a875bce9563f3b9351ebecde9b0eb1287beb50e 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftOfflinePlayer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftOfflinePlayer.java
+@@ -54,6 +54,13 @@ public class CraftOfflinePlayer implements OfflinePlayer, ConfigurationSerializa
+         return this.getPlayer() != null;
+     }
+ 
++    // Paper start
++    @Override
++    public boolean isConnected() {
++        return false;
++    }
++    // Paper end
++
+     @Override
+     public String getName() {
+         Player player = this.getPlayer();
+diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
+index 458c7039bddf63a0affbf14c24ba73d66cc13fac..5b5167947c82ca66a89aab456a2eb5b523887d33 100644
+--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
++++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
+@@ -243,6 +243,13 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
+         return this.server.getPlayer(this.getUniqueId()) != null;
+     }
+ 
++    // Paper start
++    @Override
++    public boolean isConnected() {
++        return !this.getHandle().hasDisconnected();
++    }
++    // Paper end
++
+     @Override
+     public InetSocketAddress getAddress() {
+         if (this.getHandle().connection == null) return null;