Correct cart_item_id source for address items

[`\Magento\Quote\Model\Quote\Address::getAllItems`](https://github.com/magento/magento2/blob/cf4dc427fed594f74b7168735ee1eb93febfc143/app/code/Magento/Quote/Model/Quote/Address.php#L592-L636) returns
`\Magento\Quote\Model\Quote\Address\Item[]` when the quote has multiple
shipping addresses and `Magento\Quote\Model\Quote\Item[]` with a single
shipping address. These objects have different methods for accessing the quote
item id and both variants need to be accommodated in the extractor.

Fixes magento/graphql-ce#822

Author: pmclain

app/code/Magento/QuoteGraphQl/Model/Cart/ExtractQuoteAddressData.php

@@ -61,8 +61,14 @@ public function execute(QuoteAddress $address): array
 
         $addressItemsData = [];
         foreach ($address->getAllItems() as $addressItem) {
+            if ($addressItem instanceof \Magento\Quote\Model\Quote\Item) {
+                $itemId = $addressItem->getItemId();
+            } else {
+                $itemId = $addressItem->getQuoteItemId();
+            }
+
             $addressItemsData[] = [
-                'cart_item_id' => $addressItem->getQuoteItemId(),
+                'cart_item_id' => $itemId,
                 'quantity' => $addressItem->getQty()
             ];
         }

dev/tests/api-functional/testsuite/Magento/GraphQl/Quote/Guest/GetAvailableShippingMethodsTest.php

@@ -139,29 +139,33 @@ private function getQuery(string $maskedQuoteId): string
 query {
   cart (cart_id: "{$maskedQuoteId}") {
     shipping_addresses {
-        available_shipping_methods {
-          amount {
-            value
-            currency
-          }
-          base_amount {
-            value
-            currency
-          }
-          carrier_code
-          carrier_title
-          error_message
-          method_code
-          method_title
-          price_excl_tax {
-            value
-            currency
-          }
-          price_incl_tax {
-            value
-            currency
-          }
+      cart_items {
+        cart_item_id
+        quantity
+      }
+      available_shipping_methods {
+        amount {
+          value
+          currency
         }
+        base_amount {
+          value
+          currency
+        }
+        carrier_code
+        carrier_title
+        error_message
+        method_code
+        method_title
+        price_excl_tax {
+          value
+          currency
+        }
+        price_incl_tax {
+          value
+          currency
+        }
+      }
     }
   }
 }