Issue #3307310 by Spokje: Restructure core/modules/editor/tests/modules test modules

...vate_test/config/install/editor.editor.private_images.yml

...vate_test/config/install/filter.format.private_images.yml

.../modules/editor_private_test/editor_private_test.info.yml

.../modules/editor_test/config/schema/editor_test.schema.yml

...les/editor/tests/modules/editor_test/editor_test.info.yml

...ditor/tests/modules/editor_test/editor_test.libraries.yml

...dules/editor/tests/modules/editor_test/editor_test.module

...ests/modules/editor_test/src/EditorXssFilter/Insecure.php

...ests/modules/editor_test/src/Plugin/Editor/TRexEditor.php

...s/modules/editor_test/src/Plugin/Editor/UnicornEditor.php

...est/src/Plugin/Field/FieldType/EditorTestTextLongItem.php