i18n: rename some keys, remove duplicate keys

src/Controller/ElementFormController.php

templates/directory/directory.html.twig

...element-form/form-partials/checkbox-radio-group.html.twig

templates/element-form/form-partials/elements.html.twig

templates/element-form/form-partials/select.html.twig

...lates/element-form/form-partials/taxonomy-field.html.twig

templates/header.html.twig

translations/messages+intl-icu.fr.yaml