Cannot use relationship for rendered entity on Views

Problem/Motivation

You cannot create a view and try to list rendered entities using relationship.

Steps to reproduce (based on Standard profile):

1. Add an entity reference field named "field_content" to the "page" content type. Allow content > article references.
2. Create and edit a content view.
3. Add a relationship for "Content using field_content." or "Content referenced from field_content."
4. The row style plugin is "Content" by default.
5. Click on "Teaser" in order to change the view mode, nothing happens.
6. You can't choose a view mode even if you don't want to actually use a relationship, just having one on your view triggers this.

The problem is a fatal AJAX error triggered when RowPluginBase::buildOptionsForm() calls RelationshipPluginBase::init() while providing a wrong argument type (Array instead of DisplayPluginBase).

Argument 2 passed to Drupal\views\Plugin\views\relationship\RelationshipPluginBase::init() must be an instance of Drupal\views\Plugin\views\display\DisplayPluginBase, array given, called in /app/web/core/modules/views/src/Plugin/views/row/RowPluginBase.php on line 93

Proposed resolution

Fix it, by passing along the relationship as needed and using it.

Remaining tasks

None.

User interface changes

None

API changes

None