fix: #3635920 SqlContentEntityStorage::initTableLayout() does not reset langcode keys

Julian Pustkuchenrequested to merge
issue/drupal-3635920:3635920-sqlcontententitystorageinittablelayout-does-not into main

Converting an entity type without a langcode entity key to translatable failed while copying the data, as the storage kept the langcode keys of the new definition after switching back to the original one.

Co-Authored-By: Claude Opus 5.5 noreply@anthropic.com

Closes #3635920

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