Issue #1757452 by amateescu, Xano, chx: Support config entities in entity reference fields.

core/lib/Drupal/Core/Entity/EntityManager.php

...re/Entity/Plugin/field/field_type/EntityReferenceItem.php

...upal/entity_reference/ConfigurableEntityReferenceItem.php

...rence/Plugin/entity_reference/selection/SelectionBase.php

...tity_reference/Plugin/field/widget/AutocompleteWidget.php

..._reference/Plugin/field/widget/AutocompleteWidgetBase.php

...rupal/entity_reference/Tests/EntityReferenceAdminTest.php

...entity_reference/Tests/EntityReferenceIntegrationTest.php

...Drupal/entity_reference/Tests/EntityReferenceItemTest.php

...d/Plugin/Type/FieldType/ConfigEntityReferenceItemBase.php

...ystem/lib/Drupal/system/Tests/TypedData/TypedDataTest.php

...ext/lib/Drupal/text/Tests/Formatter/TextPlainUnitTest.php

...modules/views/lib/Drupal/views/Tests/QueryGroupByTest.php