Extract code snippets from how-to-insert-a-new-slide-into-a-presentation.md

Extract the code snippets from [docs/presentation/how-to-insert-a-new-slide-into-a-presentation.md](https://github.com/OfficeDev/open-xml-docs/blob/main/docs/presentation/how-to-insert-a-new-slide-into-a-presentation.md) and use docfx snippets to retrieve them from the samples folder and audit the text.