Returns libraries to be attached.
Because this is a method, plugins can dynamically choose to attach a different library for different configurations, instead of being forced to always use the same method.
\Drupal\editor\Plugin\Core\Entity\Editor $editor: A configured text editor object.
array An array of libraries that will be added to the page for use by this text editor.
EditorManager::getAttachments()
function getLibraries(Editor $editor);