WebformInheritTask does not correctly inherit files

[jekuaitk]

Summary

The WebformInherit-task does not correctly handle inheriting file-elements data.

Reproduce

1. Create a Maestro flow with a WebformInherit-task that inherits an earlier submission.
2. Add a file element, say document_file, with a limit of one file to both webforms.
3. Open the inherit task and see in the logs that something went wrong.

Warning: foreach() argument must be of type array|object, string given in Drupal\file\Element\ManagedFile::valueCallback()

Cause

MaestroWebformInheritTask::webformSubmissionFormAlter() inherits submission data by setting default values. When a singular file is uploaded the submission data value is a string.

Default value expects an array, c.f. WebformManagedFileBase::setDefaultValue().

Fix

Cast to array when default value is being set on any type of file element.

Test

Same as reproduce but with different result:

1. Create a Maestro flow with a WebformInherit-task that inherits an earlier submission.
2. Add a file element, say document_file, with a limit of one file to both webforms.
3. Open the inherit task and see that the file is correctly inherited.