Mismatched field definition for oe_timeline in 2.x branch

[donquixote]

Follow-up to #500.

Symptoms

After upgrading to Drupal 9 / oe_content 2.x, we have the following error in status report:

The node.oe_timeline field needs to be updated.

Investigation

I found that:

• 'oe_content' contains a 'oe_content_timeline_field' module.
• This module defines a field type 'timeline_field', in TimelineFieldItem.
• It also defines field a storage definition using this field type: field.storage.node.oe_timeline.yml
  This is used by optional node types from optional submodules.
• In the new version, the schema for the field type changes.
  The new version also has an upgrade hook, oe_content_timeline_field_update_8101(). This attempts to upgrade all existing field storages using this field type.

On our site, the upgrade hook successfully upgraded a field_oe_timeline field for paragraphs, but failed to upgrade the field storage definition for the oe_timeline field on node ct.

The reason: On our site, the field has no field instances, because none of the optional node modules are enabled.

The update hook uses $timeline_fields = $entity_field_manager->getFieldMapByFieldType('timeline_field');, but this misses field storages with no instances.