[IMP] base_jsonify: Allow to export many2one and referene field as simple field

Before this change, the result of the export of a relational field was always a dict or a list of dict.

ex:

<record id="ir_exp_shopinvader_variant_lang" model="ir.exports.line">
  <field name="name">publication_language_id/name</field>
  <field name="alias">publication_language_id/name:lang</field>
  <field name="export_id" ref="shopinvader.ir_exp_shopinvader_variant" />
</record>

will output:
{
    ...
    "publication_language_id" : {
        "lang": "French"
    }
    ...
}

After this change it's now possible to define simple exporter for relational fields where the value into the result will be the display_name or a list of display_name of the related records.

ex:

<record id="ir_exp_shopinvader_variant_lang" model="ir.exports.line">
  <field name="name">publication_language_id</field>
  <field name="alias">publication_language_id:lang</field>
  <field name="export_id" ref="shopinvader.ir_exp_shopinvader_variant" />
</record>

will output:
{
    "lang": "French"
}

(Cherry-pick of 652c0167a after this commit was dropped by #1894's refactoring)
(+ test so that it cannot be forgotten again)

base_jsonify/models/models.py

@@ -48,6 +48,10 @@ class Base(models.AbstractModel):
             # This call also add the tzinfo into the datetime object
             value = fields.Datetime.context_timestamp(self, value)
             value = value.isoformat()
+        elif field.type in ("many2one", "reference"):
+            value = value.display_name if value else None
+        elif field.type in ("one2many", "many2many"):
+            value = [v.display_name for v in value]
         return value
 
     @api.model

base_jsonify/tests/test_get_parser.py

@@ -283,6 +283,33 @@ class TestParser(SavepointCase):
         json = self.category.jsonify(export.get_json_parser())[0]
         self.assertEqual(json, {"name": "yeah!"})
 
+    def test_export_relational_display_names(self):
+        """If we export a relational, we get its display_name in the json."""
+        parser = [
+            "state_id",
+            "country_id",
+            "category_id",
+            "user_ids",
+        ]
+        expected_json = {
+            "state_id": None,
+            "country_id": "France",
+            "category_id": ["Inovator"],
+            "user_ids": [],
+        }
+
+        json_partner = self.partner.jsonify(parser, one=True)
+
+        self.assertDictEqual(json_partner, expected_json)
+
+    def test_export_reference_display_names(self):
+        """Reference work the same as relational"""
+        menu = self.env.ref("base.menu_action_res_users")
+
+        json_menu = menu.jsonify(["action"], one=True)
+
+        self.assertDictEqual(json_menu, {"action": "Users"})
+
     def test_bad_parsers(self):
         bad_field_name = ["Name"]
         with self.assertRaises(KeyError):