Improve performance of getData retrieval

The getData() method is called hundred of thousand of times on PLP's without block_cache. Even when everything is cached without FPC, this method can be called thousands of times. A more direct retrieval of data and avoiding extra function calls benefits performance quite a bit. The following performance gains are monitored from a local environment in production mode:

Former setup PLP without block_html:
TIMER: 448.403317 ms
COUNT AMOUNT: 284881x

New setup PLP without block_html:
TIMER: 251.413533 ms
COUNT AMOUNT: 284881x

Former setup PLP with block_html
TIMER: 31.084917 ms
COUNT AMOUNT: 16310x

New setup PLP with block_html:
TIMER: 13.384665 ms
COUNT AMOUNT: 16310x

Author: igorwulff

lib/internal/Magento/Framework/DataObject.php

@@ -128,11 +128,10 @@ public function getData($key = '', $index = null)
             return $this->_data;
         }
 
-        /* process a/b/c key as ['a']['b']['c'] */
-        if ($key !== null && strpos($key, '/') !== false) {
+        $data = $this->_data[$key] ?? null;
+        if ($data === null && $key !== null && strpos($key, '/') !== false) {
+           /* process a/b/c key as ['a']['b']['c'] */
             $data = $this->getDataByPath($key);
-        } else {
-            $data = $this->_getData($key);
         }
 
         if ($index !== null) {