Add CodeEditor support for GeoJson pages

[dexgs]

If the Code Editor extension is enabled, it should be possible to use it to edit GeoJson pages instead of the default plaintext editor.

The Template Styles extension implements this like so: https://github.com/wikimedia/mediawiki-extensions-TemplateStyles/blob/master/includes/CodeEditorHooks.php

Could such a solution be implemented in the Maps extension?