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/0446-Add-getOfflinePlayerIfCached-String.patch

@@ -0,0 +1,39 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: oxygencraft <21054297+oxygencraft@users.noreply.github.com>
+Date: Sun, 25 Oct 2020 18:34:50 +1100
+Subject: [PATCH] Add getOfflinePlayerIfCached(String)
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+index c05fd6a179e8d142b3f5a8977ae7afab8c609a4e..c353f7a3a9ad0099ef7330dde988d1a174a0e327 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+@@ -1921,6 +1921,28 @@ public final class CraftServer implements Server {
+         return result;
+     }
+ 
++    // Paper start
++    @Override
++    @Nullable
++    public OfflinePlayer getOfflinePlayerIfCached(String name) {
++        Preconditions.checkArgument(name != null, "Name cannot be null");
++        Preconditions.checkArgument(!name.isEmpty(), "Name cannot be empty");
++
++        OfflinePlayer result = getPlayerExact(name);
++        if (result == null) {
++            GameProfile profile = console.getProfileCache().getProfileIfCached(name);
++
++            if (profile != null) {
++                result = getOfflinePlayer(profile);
++            }
++        } else {
++            offlinePlayers.remove(result.getUniqueId());
++        }
++
++        return result;
++    }
++    // Paper end
++
+     @Override
+     public OfflinePlayer getOfflinePlayer(UUID id) {
+         Preconditions.checkArgument(id != null, "UUID id cannot be null");