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>

submodule-config.c

@@ -743,8 +743,8 @@ static const struct submodule *config_from(struct submodule_cache *cache,
 	if (submodule)
 		goto out;
 
-	config = repo_read_object_file(the_repository, &oid, &type,
-				       &config_size);
+	config = odb_read_object(the_repository->objects, &oid,
+				 &type, &config_size);
 	if (!config || type != OBJ_BLOB)
 		goto out;