fix: use showFileAtRefBase64 to read per-commit file contents (#3744)

* 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>

src/utils.ts

@@ -126,16 +126,6 @@ export function readFile(path: string): string {
   return fs.readFileSync(path, 'utf-8')
 }
 
-export function readFileBase64(pathParts: string[]): string {
-  const resolvedPath = path.resolve(...pathParts)
-  if (fs.lstatSync(resolvedPath).isSymbolicLink()) {
-    return fs
-      .readlinkSync(resolvedPath, {encoding: 'buffer'})
-      .toString('base64')
-  }
-  return fs.readFileSync(resolvedPath).toString('base64')
-}
-
 /* eslint-disable  @typescript-eslint/no-explicit-any */
 function hasErrorCode(error: any): error is {code: string} {
   return typeof (error && error.code) === 'string'