Transform quote address country code to uppercase

Fixes magento/graphql-ce#658

Magento countryIds are uppercase and storing country_id as lowercase in quote
address items can cause undesired behavior when the Directory module determines
if a region is allowed for a given country.

Specifically this check fails when fetching the region code for a quote
address:
https://github.com/magento/graphql-ce/blob/a2fc3b98bf52ff7741579d16042b9c6376ecebfc/app/code/Magento/Customer/Model/Address/AbstractAddress.php#L400

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

@@ -74,6 +74,7 @@ public function execute(ContextInterface $context, CartInterface $cart, array $s
         }
 
         if (null === $customerAddressId) {
+            $addressInput['country_code'] = strtoupper($addressInput['country_code']);
             $shippingAddress = $this->quoteAddressFactory->createBasedOnInputData($addressInput);
         } else {
             $customer = $this->getCustomer->execute($context);