codeintel: expose code intel info for `GitTree`
Created by: Strum355
Closes #31074 (closed)
This is an initial pass that takes a directory in isolation into account in a relatively crude way (file-basis). There is a lot of room for expansion into walking up the paths to determine project structures etc
Test plan
Tested by hand in the API console. The brunt of the work was done and tested as part of https://github.com/sourcegraph/sourcegraph/pull/31442