Fix MCUtils and other calls to postTaskOnMain

Method changed changed it's role to providing a TickTask object which
isn't automatically scheduled onto the server

Spigot-Server-Patches/Fix-CB-call-to-changed-postToMainThread-method.patch

@@ -0,0 +1,20 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Shane Freeder <theboyetronic@gmail.com>
+Date: Fri, 10 May 2019 18:38:19 +0100
+Subject: [PATCH] Fix CB call to changed postToMainThread method
+
+
+diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
+index 4dcfc423c..8c663f90c 100644
+--- a/src/main/java/net/minecraft/server/PlayerConnection.java
++++ b/src/main/java/net/minecraft/server/PlayerConnection.java
+@@ -0,0 +0,0 @@ public class PlayerConnection implements PacketListenerPlayIn {
+ 
+         this.networkManager.getClass();
+         // CraftBukkit - Don't wait
+-        minecraftserver.postToMainThread(networkmanager::handleDisconnection);
++        minecraftserver.scheduleOnMain(networkmanager::handleDisconnection); // Paper
+     }
+ 
+     @Override
+--