Change event priority to HIGHEST

See the comments in a802f25dd6 -
effectively we want to make sure we arrive before any other thing which
may capture items (some magnet mods, etc...).

src/main/java/dan200/computercraft/shared/util/DropConsumer.java

@@ -89,7 +89,7 @@ private static void handleDrops( ItemStack stack )
         if( !remaining.isEmpty() ) remainingDrops.add( remaining );
     }
 
-    @SubscribeEvent( priority = EventPriority.LOWEST )
+    @SubscribeEvent( priority = EventPriority.HIGHEST )
     public static void onEntitySpawn( EntityJoinWorldEvent event )
     {
         // Capture any nearby item spawns