#3591693: Validate `LanguageConfigOverride`s (targeting translatable Canvas config entities) saves against config schema

1. All LanguageConfigOverrides (if any) for a Canvas config entity are validated whenever $canvas_config_entity->getTypedData()->validate() occurs, similar to core's \Drupal\content_translation\Plugin\Validation\Constraint\ContentTranslationSynchronizedFieldsConstraintValidator
2. To ensure nothing slips through the cracks, also perform this validation at save time in Canvas' tests, similar to core's \Drupal\Core\Config\Development\ConfigSchemaChecker

AI-accelerated: Yes

Testing instructions

• CI still passes
• Translate a ContentTemplate component tree using TMGMT or Config Translation and observe it works
• Translate a Page component tree using TMGMT or Config Translation and observe it works

Closes #3591693 (closed)