Stop using $error->arrayPropertyPath

Charchil Khandelwal → made their first commit to this issue’s fork.

Argh, I just stumbled on this, more specifically the issue described in 🐛 Constraints on paragraph field highlight all fields in paragraph Needs review .
I think the approach here makes more sense since arrayPropertyPath is deprecated.

But patch #2 is not working for me: it doesn't remove the delta and doesn't pass the full path.
I have the following violation path: $delta.subform.my_date_field.widget
The delta should be removed just like \Drupal\Core\Field\WidgetBase::flagErrors does:

// Separate violations by delta.
$property_path = explode('.', $violation->getPropertyPath());
$delta = array_shift($property_path);
...
$violation->arrayPropertyPath = $property_path;

Because it later passes the $delta_element to WidgetBase::errorElement
This way NestedArray::getValue() would get ['subform', 'my_date_field', 'widget'] which is correct and returns the sub-element properly.