Mixed-orientation PDF support

We have a need for mixed-orientation PDFs (some sections in portrait, others in landscape). In order to support this, I believe we need to add an `orientation` attribute to `<cfdocumentsection>`.

We are going to explore doing this in the PDF extension. If we can get this feature added, I hope that it will be acceptable to merge so others can use it as well! We're aware that we'd need to implement the feature in both the classic and modern PDF engines.