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/0460-More-lightning-API.patch

@@ -0,0 +1,37 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Nassim Jahnke <nassim@njahnke.dev>
+Date: Sun, 26 Jul 2020 14:44:09 +0200
+Subject: [PATCH] More lightning API
+
+== AT ==
+public net.minecraft.world.entity.LightningBolt life
+public net.minecraft.world.entity.LightningBolt flashes
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftLightningStrike.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftLightningStrike.java
+index 0b2ba5c93355a5b7548d4634d964732e45477a34..6fed8075aa75e3852dc826a45ca44603c0446a56 100644
+--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftLightningStrike.java
++++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftLightningStrike.java
+@@ -66,4 +66,23 @@ public class CraftLightningStrike extends CraftEntity implements LightningStrike
+         return this.spigot;
+     }
+     // Spigot end
++
++    // Paper start
++    @Override
++    public int getFlashCount() {
++        return getHandle().flashes;
++    }
++
++    @Override
++    public void setFlashCount(int flashes) {
++        com.google.common.base.Preconditions.checkArgument(flashes >= 0, "Flashes has to be a positive number!");
++        getHandle().flashes = flashes;
++    }
++
++    @Override
++    public @org.jetbrains.annotations.Nullable org.bukkit.entity.Entity getCausingEntity() {
++        final var cause = this.getHandle().getCause();
++        return cause == null ? null : cause.getBukkitEntity();
++    }
++    // Paper end
+ }