Drupal\Core\Extension\Discovery\RecursiveExtensionFilterIterator protected array members have been renamed to remove "whitelist" and "blacklist"

The Drupal\Core\Extension\Discovery\RecursiveExtensionFilterIterator class (see core/lib/Drupal/Core/Extension/Discovery/RecursiveExtensionFilterIterator.php) used to have protected array member variables called $whitelist and $blacklist. Since these phrases are both an historic bad labelling of people with racist connotations, and ambiguous and imprecise from a technical standpoint, the member arrays have been renamed:

• $blacklist is replaced with $skippedFolders
• $whitelist is replaced with $allowedExtensionTypes

Any site that has extended this class in custom code should make sure they're not using the old names for these member variables.