fsck: make "fsck_error" callback generic

fsck: make "fsck_error" callback generic

The "fsck_error" callback is designed to report the objects-related
error messages. It accepts two parameter "oid" and "object_type" which
is not generic. In order to provide a unified callback which can report
either objects or refs, remove the objects-related parameters and add
the generic parameter "void *fsck_report".

Create a new "fsck_object_report" structure which incorporates the
removed parameters "oid" and "object_type". Then change the
corresponding references to adapt to new "fsck_error" callback.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>