Following {T254478}, the TemplateData dialog now has a maps panel, with a multiline text input widget containing the maps object as a JSON string. The text input widget is disabled.
This task is for enabling the text input widget and making the JSON editable. (Changing the format to something simpler than JSON will be done in a future task.)
Acceptance criteria:
* The multiline text input is enabled
* On clicking the "Done" action, if* As the input contains a valid maps objectuser types, the model will be updated with any changes made"Done" action becomes disabled is the JSON is invalid
* On clicking the "Done" action, if* As the input contains an invalid maps objectuser types, an error message will be shownthe "Done" action becomes enabled if the JSON is valid
* On clicking the "Done" action, then the "Apply" action, the changes appear in the wikitext area when the dialog closes
* On clicking the "Back" action, the model will revert to the state before the maps panel was opened, the model will not be updated and any changes will be discarded