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/0619-Left-handed-API.patch

@@ -0,0 +1,27 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: William Blake Galbreath <blake.galbreath@gmail.com>
+Date: Thu, 14 Oct 2021 12:36:58 -0500
+Subject: [PATCH] Left handed API
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftMob.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftMob.java
+index ae430c36ed433e337dd92f197f1717fbf00ac0e1..ad293ad9d5dcd7836a4fa29b4b687346e3ae516c 100644
+--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftMob.java
++++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftMob.java
+@@ -147,6 +147,16 @@ public abstract class CraftMob extends CraftLivingEntity implements Mob {
+     public int getMaxHeadPitch() {
+         return getHandle().getMaxHeadXRot();
+     }
++
++    @Override
++    public boolean isLeftHanded() {
++        return getHandle().isLeftHanded();
++    }
++
++    @Override
++    public void setLeftHanded(boolean leftHanded) {
++        getHandle().setLeftHanded(leftHanded);
++    }
+     // Paper end
+ 
+     // Paper start