Add backwards compatibility layer for entity display default config that lacks 'type'

Problem/Motivation

Another follow-up to #2796581: Fields must store their region in entity displays.
Somehow not caught in #2809527: Add backwards compatibility layer for entity display default config that lacks 'region'.

For extra fields that are included in default config, their initial loading will trigger

Undefined index: type in Drupal\field_ui\Form\EntityDisplayFormBase->determineComponentAction() (line 664 of core/modules/field_ui/src/Form/EntityDisplayFormBase.php)

Proposed resolution

There is code to handle extra fields, but does not correctly handle them if it is coming from default config.

Remaining tasks

Write tests

User interface changes

N/A

API changes

N/A

Data model changes

N/A