BC break on embedded crud controllers

[Seb33300]

Same as #7480 (previous issue was closed)

Inside an embedded crud controller, we expect $this->getContext()->getEntity()->getInstance() to return the entity instance of the current context (the current page), not the entity instance of the embedded crud controller.

This issue was introduced by #7401.
Since that change, $this->getContext()->getEntity()->getInstance() is now always returning null when using embedded crud controller with CollectionField.