Support --include-before-body and --include-after-body with DOCX writer

Refer to #4720.  John have you considered leveraging Word's [subdocument](https://answers.microsoft.com/en-us/msoffice/forum/all/how-to-create-and-work-with-subdocuments-in/ecfc96fc-1fe4-4309-86b7-2cfff59cad2f) mechanism to make this possible?