Maintenance release covering:
Issue #1589810 by Alan D.: Import integration for Countries Additional Codes sandbox.
Issue #1460246 by Alan D.: Updated the continents with the UN Continental Regions and Sub-regions.
Issue #1589810 by Alan D.: Follow up on test fixes introduced by a) new country updates b) fixing default_value property on import c) bug fix on the enabled field being ignored in the modified refactored import.
Issue #1589810 by johnv, Alan D.: Fixed invalid filter bypass on countries.
Issue 1653306 by becw, Alan D.: Remove type hint StdClass in MigrateCountryFieldHandler::prepare()
Issue #1609150 by webflo: Added Support entity label (and callback).
(no issue) by Alan D.: Diff 7.x-3.x field support.
Issue 1662936 by ocsilalala, Alan D.: Invalid ISO3 issues, (Views passing in empty codes, possible deleted custom countries).
Issue #1609122 by webflo: Removed broken field relationship in views.
Issue #1620276 by Alan D., ChoY, et al: Making the Continent Country widget more robust in relation to FAPI position and AJAX callbacks.
Issue #1772486 by no2e: Use Package 'Example modules' for 'Countries Example' module.
Issue 1832740 by mikeryan: Class registration for Migrate 2.5 or later.
Issue 1793392 by cristiroma, Alan D.: Official name changes.