ckeditor extension: Custom inline elements are not upcasted correctly in tables (tableCell) and with `autoparagraph: false` in $root

[mhsdesign]

See https://github.com/ckeditor/ckeditor5/issues/6698#issuecomment-639243844 for more detail.

This bug is fixed via https://github.com/ckeditor/ckeditor5/issues/7753 in Ckeditor 22 but we still use 16

There is a workaround described here: https://github.com/ckeditor/ckeditor5/issues/6698#issuecomment-1262704379

The question is if we should add this fix/workaround into our codebase? (This would be a better option that multiple people defining this themselves -> which is unlikely but still ...)