6 classes are annotated with CKEditorPlugin

Internal in drupal/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/CKEditorPlugin/Internal.php
Defines the "internal" plugin (i.e. core plugins part of our CKEditor build).
Llama in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/Llama.php
Defines the "Llama" plugin, with a CKEditor "llama" feature.
LlamaButton in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/LlamaButton.php
Defines a "LlamaButton" plugin, with a toolbar builder-enabled "llama" feature.
LlamaContextual in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/LlamaContextual.php
Defines a "Llama" plugin, with a contextually enabled "llama" feature.
LlamaContextualAndButton in drupal/core/modules/ckeditor/tests/modules/lib/Drupal/ckeditor_test/Plugin/CKEditorPlugin/LlamaContextualAndButton.php
Defines a "LlamaContextualAndbutton" plugin, with a contextually OR toolbar builder-enabled "llama" feature.
StylesCombo in drupal/core/modules/ckeditor/lib/Drupal/ckeditor/Plugin/CKEditorPlugin/StylesCombo.php
Defines the "stylescombo" plugin.