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/0591-Add-PlayerArmSwingEvent.patch

@@ -0,0 +1,19 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jake Potrebic <jake.m.potrebic@gmail.com>
+Date: Fri, 12 Mar 2021 19:22:21 -0800
+Subject: [PATCH] Add PlayerArmSwingEvent
+
+
+diff --git a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+index 75ff85e3710d5e70a32fe39e8469c1f169fd2d46..bce87f55ad85837a17f783b5341ef5b64ab0ede0 100644
+--- a/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
++++ b/src/main/java/net/minecraft/server/network/ServerGamePacketListenerImpl.java
+@@ -2328,7 +2328,7 @@ public class ServerGamePacketListenerImpl extends ServerCommonPacketListenerImpl
+         } // Paper end - Call interact event
+ 
+         // Arm swing animation
+-        PlayerAnimationEvent event = new PlayerAnimationEvent(this.getCraftPlayer(), (packet.getHand() == InteractionHand.MAIN_HAND) ? PlayerAnimationType.ARM_SWING : PlayerAnimationType.OFF_ARM_SWING);
++        io.papermc.paper.event.player.PlayerArmSwingEvent event = new io.papermc.paper.event.player.PlayerArmSwingEvent(this.getCraftPlayer(), org.bukkit.craftbukkit.CraftEquipmentSlot.getHand(packet.getHand())); // Paper - Add PlayerArmSwingEvent
+         this.cserver.getPluginManager().callEvent(event);
+ 
+         if (event.isCancelled()) return;