Cross-repo code navigation for Python projects

Cross-repo code navigation is now available for all Python repositories. When showing the definition of a function or method, we now include definitions from other repositories, and from the Python standard library.

Cross-repo code navigation is powered by the stack graphs framework and by the Dependency Graph. You can read about how we use stack graphs for code navigation and visit the stack-graphs repo to learn more. You can also read more about code navigation for Python and other languages in our documentation.