[PP-1] Deprecate \Drupal\ckeditor5\Plugin\Editor\CKEditor5::validatePair() and `type: ckeditor5_valid_pair__format_and_editor`

Zero Functional test failures now 👍

It's thanks to the very detailed test coverage in \Drupal\Tests\ckeditor5\Kernel\ValidatorsTest that a critical oversight in ConfigEntityAdapter was discovered. 🫣

#1818574: Support config entities in typed data EntityAdapter → introduced \Drupal\KernelTests\Core\Entity\ConfigEntityAdapterTest::testValidate(), but it is inadequate. We need additional test coverage, and this probably should be handled in its own issue.

See https://git.drupalcode.org/project/drupal/-/merge_requests/6892/diffs?co... for the relevant changes.

This blocks 🌱 [META] Discuss: merge the Editor config entity into the FilterFormat config entity Active .

This also blocks the Recipes initiative at #3401925: After a recipe is successfully applied, validate all of the config that was imported or modified by config actions → .

Follow-up created: 🐛 Config validation: config entities should get the same validation errors when validated as plain config vs ConfigEntityAdapter Needs review . Pushed it forward far enough that it's now clear that that will work, and that it SHOULD happen ASAP.

All of the changes that the current MR makes outside of core/modules/ckeditor5 will disappear from this MR once 🐛 Config validation: config entities should get the same validation errors when validated as plain config vs ConfigEntityAdapter Needs review lands. So ceasing all work on this MR until that lands 👍