On open repository open common cat file batch and batch-check (#15667)

Use common git cat-file --batch and git cat-file --batch-check to
significantly reduce calls to git.
    
Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/repo_blob_nogogit.go

@@ -11,7 +11,7 @@ func (repo *Repository) getBlob(id SHA1) (*Blob, error) {
 		return nil, ErrNotExist{id.String(), ""}
 	}
 	return &Blob{
-		ID:       id,
-		repoPath: repo.Path,
+		ID:   id,
+		repo: repo,
 	}, nil
 }