Code Modernization: Use instanceof instead of a comparison with get_class().

Includes adjusting external libraries which are no longer maintained externally.

Props jrf.
See #50767.

git-svn-id: https://develop.svn.wordpress.org/trunk@49194 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-json.php

@@ -918,7 +918,7 @@ class Services_JSON
 
         if (class_exists('pear')) {
             return PEAR::isError($data, $code);
-        } elseif (is_object($data) && (get_class($data) == 'services_json_error' ||
+        } elseif (is_object($data) && ($data instanceof services_json_error ||
                                  is_subclass_of($data, 'services_json_error'))) {
             return true;
         }