Fixing Import counts when multiple bunches

Changing updateItemsCounterStats to add and assign instead of just assign.
This is to fix bug where only the last bunch counts (instead of all bunch counts) were being returned to user.

Author: JacobBrownAustin

app/code/Magento/ImportExport/Model/Import/AbstractEntity.php

@@ -891,9 +891,9 @@ public function getDeletedItemsCount()
      */
     protected function updateItemsCounterStats(array $created = [], array $updated = [], array $deleted = [])
     {
-        $this->countItemsCreated = count($created);
-        $this->countItemsUpdated = count($updated);
-        $this->countItemsDeleted = count($deleted);
+        $this->countItemsCreated += count($created);
+        $this->countItemsUpdated += count($updated);
+        $this->countItemsDeleted += count($deleted);
         return $this;
     }