Fix SKU limit in import new products for 2.3 with backward compatible

Author: ravi-chandra3197

app/code/Magento/CatalogImportExport/Model/Import/Product/Validator.php

@@ -7,6 +7,7 @@
 
 use Magento\CatalogImportExport\Model\Import\Product;
 use Magento\Framework\Validator\AbstractValidator;
+use Magento\Catalog\Model\Product\Attribute\Backend\Sku;
 
 /**
  * Class Validator
@@ -69,6 +70,8 @@ protected function textValidation($attrCode, $type)
         $val = $this->string->cleanString($this->_rowData[$attrCode]);
         if ($type == 'text') {
             $valid = $this->string->strlen($val) < Product::DB_MAX_TEXT_LENGTH;
+        } else if ($attrCode == Product::COL_SKU) {
+            $valid = $this->string->strlen($val) < SKU::SKU_MAX_LENGTH;
         } else {
             $valid = $this->string->strlen($val) < Product::DB_MAX_VARCHAR_LENGTH;
         }