Motivation:

• CKEditor5 has no global registry of editor instances and the current script used for setting WYSIWYG field's value no longer works if CKEditor5 is utilised. This leads to failing tests (i.e., when comparing the actual value with the expected one after filling out a WYSIWYG field)

Proposed change:

• Enable filling CKEditor5 based fields while keeping backwards compatibility with CKEditor4 (and below) if needed.
• The proposed solution checks if there is data-ckeditor5-id attribute present for the WYSIWYG field. If so, original script is overridden with CKEditor5 compatible version (see https://ckeditor.com/docs/ckeditor5/latest/examples/how-tos.html#how-to-get-the-editor-instance-object-from-the-dom-element). Therefore, we don't need any additional parameters of functions to handle CKEditor5 specifically as the existing one can decide itself which version of CKEditor is in use for the particular field and act accordingly.