* Initial work on custom field choice sets
* Rename choices to extra_choices (prep for #12194)
* Remove CustomField.choices
* Add & update tests
* Clean up table columns
* Add order_alphanetically boolean for choice sets
* Introduce ArrayColumn for choice lists
* Show dependent custom fields on choice set view
* Update custom fields documentation
* Introduce ArrayWidget for more convenient editing of choices
* Incorporate PR feedback
* Misc cleanup
* Initial work on predefined choices for custom fields
* Misc cleanup
* Add IATA airport codes
* #13241: Add support for custom field choice labels
* Restore ArrayColumn
* Misc cleanup
* Change extra_choices back to a nested ArrayField to preserve choice ordering
* Hack to bypass GraphQL API test utility absent support for nested ArrayFields
