MAGETWO-69733: add middle name to checkout address html templates #8878 #8879

 - Merge Pull Request #8879 from ajpevers/magento2:issue-8878
 - Merged commits:
   1. f3c7406
   2. 5f1b460
   3. 3c632aa

Author: ishakhsuvarov

app/code/Magento/Checkout/Block/Checkout/AttributeMerger.php

@@ -321,6 +321,11 @@ protected function getDefaultValue($attributeCode)
                     return $this->getCustomer()->getFirstname();
                 }
                 break;
+            case 'middlename':
+                if ($this->getCustomer()) {
+                    return $this->getCustomer()->getMiddlename();
+                }
+                break;
             case 'lastname':
                 if ($this->getCustomer()) {
                     return $this->getCustomer()->getLastname();

app/code/Magento/Checkout/view/frontend/web/template/billing-address/details.html

@@ -5,7 +5,7 @@
  */
 -->
 <div class="billing-address-details" data-bind="if: isAddressDetailsVisible() && currentBillingAddress()">
-    <!-- ko text: currentBillingAddress().prefix --><!-- /ko --> <!-- ko text: currentBillingAddress().firstname --><!-- /ko -->
+    <!-- ko text: currentBillingAddress().prefix --><!-- /ko --> <!-- ko text: currentBillingAddress().firstname --><!-- /ko --> <!-- ko text: currentBillingAddress().middlename --><!-- /ko -->
     <!-- ko text: currentBillingAddress().lastname --><!-- /ko --> <!-- ko text: currentBillingAddress().suffix --><!-- /ko --><br/>
     <!-- ko text: currentBillingAddress().street --><!-- /ko --><br/>
     <!-- ko text: currentBillingAddress().city --><!-- /ko -->, <span data-bind="html: currentBillingAddress().region"></span> <!-- ko text: currentBillingAddress().postcode --><!-- /ko --><br/>

app/code/Magento/Checkout/view/frontend/web/template/shipping-address/address-renderer/default.html

@@ -5,7 +5,7 @@
  */
 -->
 <div class="shipping-address-item" data-bind="css: isSelected() ? 'selected-item' : 'not-selected-item'">
-    <!-- ko text: address().prefix --><!-- /ko --> <!-- ko text: address().firstname --><!-- /ko -->
+    <!-- ko text: address().prefix --><!-- /ko --> <!-- ko text: address().firstname --><!-- /ko --> <!-- ko text: address().middlename --><!-- /ko -->
     <!-- ko text: address().lastname --><!-- /ko --> <!-- ko text: address().suffix --><!-- /ko --><br/>
     <!-- ko text: address().street --><!-- /ko --><br/>
     <!-- ko text: address().city --><!-- /ko -->, <span data-bind="html: address().region"></span> <!-- ko text: address().postcode --><!-- /ko --><br/>

app/code/Magento/Checkout/view/frontend/web/template/shipping-information/address-renderer/default.html

@@ -5,7 +5,7 @@
  */
 -->
 <!-- ko if: (visible()) -->
-    <!-- ko text: address().prefix --><!-- /ko --> <!-- ko text: address().firstname --><!-- /ko -->
+    <!-- ko text: address().prefix --><!-- /ko --> <!-- ko text: address().firstname --><!-- /ko --> <!-- ko text: address().middlename --><!-- /ko -->
     <!-- ko text: address().lastname --><!-- /ko --> <!-- ko text: address().suffix --><!-- /ko --><br/>
     <!-- ko text: address().street --><!-- /ko --><br/>
     <!-- ko text: address().city --><!-- /ko -->, <span data-bind="html: address().region"></span> <!-- ko text: address().postcode --><!-- /ko --><br/>