Do not use ForkJoinPool common exector for creating client command struct (Fixes #6936)

patches/server/Async-command-map-building.patch

@@ -21,9 +21,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
          // CraftBukkit start
          // Register Vanilla commands into builtRoot as before
 +        // Paper start - Async command map building
-+        java.util.concurrent.ForkJoinPool.commonPool().execute(() -> {
-+            sendAsync(player);
-+        });
++        net.minecraft.server.MCUtil.scheduleAsyncTask(() -> this.sendAsync(player));
 +    }
 +
 +    private void sendAsync(ServerPlayer player) {