Investigate integrating stack graph for code navigation

[stapelberg]

GitHub recently introduced precise code navigation: https://github.blog/2021-12-09-introducing-stack-graphs/

The underlying stack-graph is open source: https://github.com/github/stack-graphs/

Their architecture sounds suitable for DCS (incremental indexing without dependencies between repositories, no setup required, etc.)

To get a better idea if/how we could leverage this for DCS, here are things to check:

• How much compute time and disk space does stack graphs require?
• How could we make available the data, given that we currently redirect to sources.d.n for browsing code?