Do not use field definitions when exporting data

Calling Model.fields_get is expensive especially for each record to export.

Closes #14061

trytond/trytond/model/modelstorage.py

@@ -886,7 +886,6 @@ class ModelStorage(Model):
                     field_name, language = field_name.split(':lang=')
                 eModel = pool.get(value.__name__)
                 field = eModel._fields[field_name]
-                field_def = eModel.fields_get()[field_name]
                 if field.states and 'invisible' in field.states:
                     invisible = _record_eval_pyson(
                         value, field.states['invisible'])
@@ -899,7 +898,7 @@ class ModelStorage(Model):
                     value = field.translated().__get__(value, eModel)(language)
                 else:
                     value = getattr(value, field_name)
-                if field_def['type'] in {'one2many', 'many2many'}:
+                if field._type in {'one2many', 'many2many'}:
                     first = True
                     child_fields_names = [(x[:i + 1] == fields_tree[:i + 1]
                             and x[i + 1:]) or [] for x in fields_names]
@@ -928,7 +927,7 @@ class ModelStorage(Model):
                 if value is None:
                     value = ''
                 elif isinstance(value, Model):
-                    if field_def['type'] == 'reference':
+                    if field._type == 'reference':
                         value = f'{value.__name__},{value.rec_name}'
                     else:
                         value = value.rec_name