All classes that implement CKEditorPluginButtonsInterface

class \Drupal\ckeditor\CKEditorPluginBase implements CKEditorPluginButtonsInterface, CKEditorPluginInterface
class \Drupal\ckeditor\Plugin\CKEditorPlugin\Internal
class \Drupal\ckeditor\Plugin\CKEditorPlugin\StylesCombo implements CKEditorPluginConfigurableInterface
class \Drupal\ckeditor_test\Plugin\CKEditorPlugin\LlamaButton implements CKEditorPluginButtonsInterface
class \Drupal\ckeditor_test\Plugin\CKEditorPlugin\LlamaContextualAndButton implements CKEditorPluginButtonsInterface, CKEditorPluginConfigurableInterface, CKEditorPluginContextualInterface