Merge branch 'po/object-id' into next

* po/object-id:
sha1_file: convert index_stream to struct object_id
sha1_file: convert hash_sha1_file_literally to struct object_id
sha1_file: convert index_fd to struct object_id
sha1_file: convert index_path to struct object_id
read-cache: convert to struct object_id
builtin/hash-object: convert to struct object_id