Issue #3635342: Stop redeclaring $languageManager in WebformEntityStorage, which core 12 types in ConfigEntityStorage

For #3635342.

Drupal core main (#3278431) declares ConfigEntityStorage::$languageManager as a typed promoted property. WebformEntityStorage redeclares it untyped, which PHP refuses: every test that boots Webform fails on Drupal 12 with "Type of Drupal\webform\WebformEntityStorage::$languageManager must be Drupal\Core\Language\LanguageManagerInterface".

This removes the redeclaration. The parent declares the property on every core Webform supports (untyped on 10.3, 10.5 and 11.x, typed on 12), and createInstance() still sets it.

AI-Generated: Yes (Claude Code was used to find the cause, write the fix and this description. I reviewed them.)