odb: rename repo_read_object_file()

Rename `repo_read_object_file()` to `odb_read_object()` to match other
functions related to the object database and our modern coding
guidelines.

Introduce a compatibility wrapper so that any in-flight topics will
continue to compile.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

tree.c

@@ -193,8 +193,8 @@ int parse_tree_gently(struct tree *item, int quiet_on_missing)
 
 	if (item->object.parsed)
 		return 0;
-	buffer = repo_read_object_file(the_repository, &item->object.oid,
-				       &type, &size);
+	buffer = odb_read_object(the_repository->objects, &item->object.oid,
+				 &type, &size);
 	if (!buffer)
 		return quiet_on_missing ? -1 :
 			error("Could not read %s",