MAGETWO-66778: Api Annotation Coverage of OMS-related Modules

- Added PHPDoc block;

Author: aakimov

app/code/Magento/GiftMessage/Block/Cart/Item/Renderer/Actions/LayoutProcessorInterface.php

@@ -8,6 +8,12 @@
 use Magento\Quote\Model\Quote\Item\AbstractItem;
 
 /**
+ * Layout processor interface.
+ *
+ * Classes that implement this interface can be used to modify cart JS layout before rendering.
+ * Interface method accepts quote item, so the required data can be easily retrieved.
+ * @see \Magento\GiftMessage\Block\Cart\Item\Renderer\Actions\GiftOptions
+ *
  * @api
  */
 interface LayoutProcessorInterface