* GitCommandManager: add a function to get a file's contents at a specific revision
* use showFileAtRef instead of readFileBase64
* Teach GitCommandManager.exec about an object of exec parameters so we can add more
* Encode the showFiletRef output as base64 out of the gate
* Fix missing async for function
* Use Buffer.concat to avoid issues with partial data streams
* formatting
---------
Co-authored-by: gustavderdrache <alex.ford@determinate.systems>
dd2324fc52