archive: convert write_archive_entry_fn_t to object_id

Convert the write_archive_entry_fn_t type to use a pointer to struct
object_id.  Convert various static functions in the tar and zip
archivers also.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>