MAGETWO-75453: [Backport] - Decimal to Float Convertion #9266 - for 2.2

 - reverted original fix due to broken logic in other parts or the system
 - added local fix for Tier Price

Author: Oleksii Korshenko

app/code/Magento/Catalog/Pricing/Price/TierPrice.php

@@ -82,7 +82,7 @@ public function __construct(
         GroupManagementInterface $groupManagement,
         CustomerGroupRetrieverInterface $customerGroupRetriever = null
     ) {
-        $quantity = $quantity ?: 1;
+        $quantity = floatval($quantity) ? $quantity : 1;
         parent::__construct($saleableItem, $quantity, $calculator, $priceCurrency);
         $this->customerSession = $customerSession;
         $this->groupManagement = $groupManagement;