Correctly copy alias requirements in command upgrader

Fixes NPE when converting namespaced commands.

Since the brigadier command api, more aliased commands
(namespaced variants) are registered in the vanilla dispatcher,
which made this issue more apparent.

patches/server/Rewrite-dataconverter-system.patch

@@ -27842,7 +27842,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +                    new LiteralCommandNode<>(
 +                        redirectNode.getName(),
 +                        null,
-+                        null,
++                        toNode.getRequirement(),
 +                        toNode,
 +                        redirectNode.getRedirectModifier(),
 +                        redirectNode.isFork()