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/handle-PacketPlayInKeepAlive-async.patch

@@ -15,7 +15,7 @@ also adding some additional logging in order to help work out what is causing
 random disconnections for clients.
 
 diff --git a/src/main/java/net/minecraft/server/PlayerConnection.java b/src/main/java/net/minecraft/server/PlayerConnection.java
-index 7a4b14f865..de34c4e3ee 100644
+index 7a4b14f86..2dd092f0a 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 {
@@ -32,7 +32,7 @@ index 7a4b14f865..de34c4e3ee 100644
          } else if (!this.isExemptPlayer()) {
 -            this.disconnect(new ChatMessage("disconnect.timeout", new Object[0]));
 +            // Paper start - This needs to be handled on the main thread for plugins
-+            minecraftServer.postToMainThread(() -> {
++            minecraftServer.scheduleOnMain(() -> {
 +                this.disconnect(new ChatMessage("disconnect.timeout"));
 +            });
 +            // Paper end