merge-recursive: convert struct merge_file_info to object_id

merge-recursive: convert struct merge_file_info to object_id

Convert struct merge_file_info to use struct object_id.  The following
Coccinelle semantic patch was used to implement this, followed by the
transformations in object_id.cocci:

@@
struct merge_file_info o;
@@
- o.sha
+ o.oid.hash

@@
struct merge_file_info *p;
@@
- p->sha
+ p->oid.hash

Signed-off-by: brian m. carlson <redacted>
Signed-off-by: Junio C Hamano <redacted>