Do not use field definitions when exporting data

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

Closes #14061
(grafted from f9886ab808fd8eb8a0334e6fb0e1f1839b4ddfe9)

--HG--
branch : 7.0

trytond/trytond/model/modelstorage.py

@@ -718,7 +718,6 @@ class ModelStorage(Model):
                     field_name, descriptor = field_name.split('.')
                 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'])
@@ -729,7 +728,7 @@ class ModelStorage(Model):
                     value = getattr(field, descriptor)().__get__(value, eModel)
                 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]