[FIX] base_address_extended: sync city_id with children contacts

Steps to reproduce:
- Install contacts and base_address_extended
- Install a module adding "res.city" records (e.g. l10n_co_edi)
- Go to Contacts and create a new one:
  * Name: [any]
  * Country: Colombia
  * City (city_id): [any]
- Create a "child" contact of "Contact" type
- Save the contact

Issue:
"city_id" field of the child contact is False.
It is not possible to set the address of a contact-type contact manually.
Some address fields ('street', 'street2', 'zip', 'city', 'state_id', 'country_id')
are synchronized with the parent contact.
"city_id" is not and is not settable at all for contact-type contact.
It could be an issue for Colombian or Mexican localizations if a child contact is
used for an invoice as some data have to be retrieved from "city_id" field to generate
the electronic invoice.

Solution:
Add "city_id" in the list of address fields to sync.

opw-3747296

closes odoo/odoo#158686

X-original-commit: ec059dfd0a3f57754bd481f0a651b01c92b10dea
Signed-off-by: Habib Ayob (ayh) <ayh@odoo.com>

addons/base_address_extended/models/res_partner.py

@@ -16,6 +16,10 @@ class Partner(models.Model):
     city_id = fields.Many2one(comodel_name='res.city', string='City ID')
     country_enforce_cities = fields.Boolean(related='country_id.enforce_cities')
 
+    @api.model
+    def _address_fields(self):
+        return super()._address_fields() + ['city_id']
+
     def _inverse_street_data(self):
         """ update self.street based on street_name, street_number and street_number2 """
         for partner in self:

addons/base_address_extended/tests/test_street_fields.py

@@ -36,3 +36,26 @@ class TestStreetFields(TransactionCase):
             partner.street_number = number
             partner.street_name = name
             self.assertEqual(partner.street, street.strip(), 'Wrongly formatted street: expected %s, received %s' % (street, partner.street))
+
+    def test_child_sync(self):
+        """ Test that city_id is propagated to (contact-type) children contacts. """
+        usa = self.env.ref('base.us')
+        new_york_city = self.env['res.city'].create({
+            'name': 'New York',
+            'country_id': usa.id,
+        })
+        parent = self.env['res.partner'].create({
+            'name': 'Parent Company',
+            'country_id': usa.id,
+            'city_id': new_york_city.id,
+        })
+        child = self.env['res.partner'].create({
+            'name': 'Child Contact',
+            'type': 'contact',
+            'parent_id': parent.id,
+        })
+        self.assertRecordValues(child, [{
+            'name': 'Child Contact',
+            'country_id': usa.id,
+            'city_id': new_york_city.id,
+        }])