For PDF landing pages (Lander project), determine the revision date metadata for an lsstdoc-based LaTeX document through these methods, in priority:
1. Date provided in \date command
2. Git timestamp for the most recent commit that affected document content.
3. Run time
This will make the revision dates posted on the document landing pages more consistent with the dates printed in the PDF. It will also prevent the post revision date from changing for administrative commits to a document's repo.