Implement custom validation constraint

Patch outdated, please re-roll it

Here's a re-roll for the patch

Should be in an MR

Actually since I added configuration validation in 3.0.x branch is this still needed?

Take my previous statement back. I've updated slightly for 10.3

Will need a review from someone else besides myself.

pavel.bulat → made their first commit to this issue’s fork.

The patch had an issue:

Error: Call to undefined method Drupal\Core\Field\BaseFieldDefinition::id() in limited_field_widgets_field_widget_third_party_settings_form() when you try to open the `Manage Form Display` tab with fields that were created on a code level.
For example: a Commerce Order has an Unlimited Order Items field. The field definition for the Order Items doesn't have id().

Steps to reproduce

1) Install Drupal Commerce and Commerce Order
2) Create a new order type
3) Open Manage Form Display tab

In the last commit, I added a check if ($field_definition instanceof FieldConfigInterface). It fixed the issue, but I am not sure that it was the right way to fix it, so feel free to review it.