New submissions (via the add form) now include the webform's default values in the submission data.

Problem

When creating or updating a submission, the webform element's #default_value and #value were not included in the submission' data. (\Drupal\webform\WebformSubmissionInterface::getData). This resulted in any computed elements or tokens that rely on another element's default value to not work as expected.

Solution

The Webform entity now has a \Drupal\webform\WebformInterface::getElementsDefaultData which extracts the #default_value and #value from every element and now \Drupal\webform\WebformSubmissionForm::setEntity will apply the default data to webform submission's data.

This change is primarily an API improvement that only affects broken edge cases and should not have an impact on existing webforms.