Value is lost for cmrf_display fields when coming back from preview

Problem/Motivation

When coming back from the form preview to the form, the values of cmrf_display fields are lost.

Steps to reproduce

Configure a webform with formprocessor handler, a default value, and a cmrf_display field for this value. Enable preview. Load the form. Load the form preview. Go back to the form.

Proposed resolution

Set default values in form state storage and load those values in \Drupal\cmrf_form_processor\WebformSubmissionHandler::alterForm() when the form is marked as submitted.