ENGCOM-3199: Update documentation for Order#getAppliedRuleIds #18573

 - Merge Pull Request #18573 from zack6849/magento2:2.3-develop
 - Merged commits:
   1. d1d5fdb
   2. cda6aa1

Author: magento-engcom-team

app/code/Magento/Sales/Api/Data/OrderInterface.php

@@ -581,6 +581,7 @@ public function getAdjustmentPositive();
     /**
      * Gets the applied rule IDs for the order.
      *
+     * Rules are comma separated if there are more than one.
      * @return string|null Applied rule IDs.
      */
     public function getAppliedRuleIds();

app/code/Magento/Sales/Api/Data/OrderItemInterface.php

@@ -415,6 +415,7 @@ public function getAmountRefunded();
     /**
      * Gets the applied rule IDs for the order item.
      *
+     * Rules are comma separated if there are more than one.
      * @return string|null Applied rule IDs.
      */
     public function getAppliedRuleIds();

app/code/Magento/Sales/Model/Order.php

@@ -2152,6 +2152,7 @@ public function getAdjustmentPositive()
     /**
      * Return applied_rule_ids
      *
+     * Rules are comma separated if there are more than one.
      * @return string|null
      */
     public function getAppliedRuleIds()

app/code/Magento/Sales/Model/Order/Item.php

@@ -725,6 +725,7 @@ public function getAmountRefunded()
     /**
      * Return applied_rule_ids
      *
+     * Rules are comma separated if there are more than one.
      * @return string|null
      */
     public function getAppliedRuleIds()