sha1_object_info_extended: pass object_info to helpers

sha1_object_info_extended: pass object_info to helpers

We take in a "struct object_info" which contains pointers to
storage for items the caller cares about. But then rather
than pass the whole object to the low-level loose/packed
helper functions, we pass the individual pointers.

Let's pass the whole struct instead, which will make adding
more items later easier.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>