Refactor git command stdio pipe (#36422)

Most potential deadlock problems should have been fixed, and new code is
unlikely to cause new problems with the new design.

Also raise the minimum Git version required to 2.6.0 (released in 2015)

modules/gitrepo/commit_file.go

@@ -67,20 +67,18 @@ func parseCommitFileStatus(fileStatus *CommitFileStatus, stdout io.Reader) {
 
 // GetCommitFileStatus returns file status of commit in given repository.
 func GetCommitFileStatus(ctx context.Context, repo Repository, commitID string) (*CommitFileStatus, error) {
-	stdout, w := io.Pipe()
+	cmd := gitcmd.NewCommand("log", "--name-status", "-m", "--pretty=format:", "--first-parent", "--no-renames", "-z", "-1")
+	stdout, stdoutClose := cmd.MakeStdoutPipe()
+	defer stdoutClose()
 	done := make(chan struct{})
 	fileStatus := NewCommitFileStatus()
 	go func() {
 		parseCommitFileStatus(fileStatus, stdout)
 		close(done)
 	}()
-
-	err := gitcmd.NewCommand("log", "--name-status", "-m", "--pretty=format:", "--first-parent", "--no-renames", "-z", "-1").
-		AddDynamicArguments(commitID).
+	err := cmd.AddDynamicArguments(commitID).
 		WithDir(repoPath(repo)).
-		WithStdout(w).
 		RunWithStderr(ctx)
-	_ = w.Close() // Close writer to exit parsing goroutine
 	if err != nil {
 		return nil, err
 	}