XWIKI-22308: The inplace editor locks the original translation when creating a new translation

* reload the edit mode when switching the edited translation
* change the document locale before locking it (taking care to restore the original translation if the edit fails for the new translation)
* when reloading the document JSON, fallback on the orignal translation if the requested translation doesn't exist
* when rendering the document, fallback on the original translation if the edited translation is new (so that we initialize the content of the new translation with the values from the original translation)

(cherry picked from commit d4b3a322)