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/0804-Ignore-impossible-spawn-tick.patch

@@ -0,0 +1,18 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: dannyball710 <dannyball710@gmail.com>
+Date: Sat, 12 Feb 2022 23:42:48 +0800
+Subject: [PATCH] Ignore impossible spawn tick
+
+
+diff --git a/src/main/java/net/minecraft/world/level/BaseSpawner.java b/src/main/java/net/minecraft/world/level/BaseSpawner.java
+index 41d2793e69bd664456b5e3c5891b03bdcb31d103..65c3e91ac4541c0150057dc9f012eb1ee566516e 100644
+--- a/src/main/java/net/minecraft/world/level/BaseSpawner.java
++++ b/src/main/java/net/minecraft/world/level/BaseSpawner.java
+@@ -82,6 +82,7 @@ public abstract class BaseSpawner {
+     }
+ 
+     public void serverTick(ServerLevel world, BlockPos pos) {
++        if (spawnCount <= 0 || maxNearbyEntities <= 0) return; // Paper - Ignore impossible spawn tick
+         // Paper start - Configurable mob spawner tick rate
+         if (spawnDelay > 0 && --tickDelay > 0) return;
+         tickDelay = world.paperConfig().tickRates.mobSpawner;