The @MigrateField plugins with plugin IDs 'email', 'entityreference' and 'number_default' have had the location of their implementing class moved, and the old plugin classes have been deprecated.
Previously they were located in the Core Field library at Drupal/Core/Field/plugin/migrate/field. Because these plugins extend classes and reference interfaces in the migrate and migrate_drupal modules, they should not be included in the core library and have been moved into the field module.
The following class changes were made:
- The 'email' plugin class has moved from \Drupal\Core\Field\Plugin\migrate\field\Email to \Drupal\field\Plugin\migrate\field\Email
- The 'entityreference' plugin class has moved from \Drupal\Core\Field\Plugin\migrate\field\d7\EntityReference to \Drupal\field\Plugin\migrate\field\d7\EntityReference
- The 'number_default' plugin class has moved from \Drupal\Core\Field\Plugin\migrate\field\d7\NumberField to \Drupal\field\Plugin\migrate\field\d7\NumberField
The plugin IDs have not changed and may continue to be referenced. Any developer extending the original classes directly should update their references to the new namespaces.