That allows locales to switch the order of the first name and last name, should they prefer to do so.
The string was previously used in `wp_insert_user()` and is now reused in other places for consistency:
* `WP_MS_Users_List_Table::column_name()`
* `WP_Users_List_Table::column_name()`
* `wp_list_authors()`
* `wp_list_users()`
Note: This also removes the `wp_list_author_full_name` filter, introduced for the same purpose in `wp_list_authors()`, as redundant for now.
Follow-up to [53486].
See #17025.
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