Issue #2357119 by claudiu.cristea, mondrake, attiks: Allow image toolkit derivatives

core/core.services.yml

...Drupal/Core/ImageToolkit/ImageToolkitOperationManager.php

core/modules/system/src/Tests/Image/ToolkitTest.php

...les/image_test/src/Plugin/ImageToolkit/DerivedToolkit.php

...image_test/src/Plugin/ImageToolkit/Operation/test/Bar.php

...image_test/src/Plugin/ImageToolkit/Operation/test/Foo.php

...est/src/Plugin/ImageToolkit/Operation/test/FooDerived.php

.../src/Plugin/ImageToolkit/Operation/test/OperationBase.php