Extract code snippets from how-to-set-a-custom-property-in-a-word-processing-document.md

[mikeebowen]

Extract the code snippets from [docs/word/how-to-set-a-custom-property-in-a-word-processing-document.md](https://github.com/OfficeDev/open-xml-docs/blob/main/docs/word/how-to-set-a-custom-property-in-a-word-processing-document.md and use docfx snippets to retrieve them from the samples folder and audit the text.