Move Media Library CKEditor 4 integrations from Media into CKEditor

Problem/Motivation

Media Library integrates with both CKEditor 4 and CKEditor 5. CKEditor 4 will be deprecated and removed from core in Drupal 10, so Media Library's integrations should be owned by the CKEditor module instead of the Media Library module.

Proposed resolution

Move all of the integration code from Media Library to CKEditor:

1. Review plugin in core/modules/medialibrary/js/plugins/drupalmedialibrary (appears to have CKEditor 4 integration) and move as appropriate
2. Move Drupal\media_library\Plugin\CKEditorPlugin to CKEditor's namespace and update accordingly. (Deprecate the old version.)
3. Look at core/modules/media_library/src/MediaLibraryEditorOpener.php which mentions CKEditor in the text. Maybe just say "text editor integration"?
4. Move the following tests to CKEditor's namespace:
   • core/modules/media_library/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
   • core/modules/media_library/tests/src/FunctionalJavascript/CKEditorIntegrationTest.php
5. Move integration code from media_library.module to (e.g.) ckeditor.module.

There is a diffstat of potential Media Library integration code to remove but it only removes the code, rather than moving it to CKEditor 4 and updating namespaces/etc.

Do not alter any CKEditor 5 Media Library integration.

Remaining tasks

TBD

User interface changes

TBD

API changes

TBD

Data model changes

TBD

Release notes snippet

TBD