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>

notes-merge.c

@@ -340,7 +340,7 @@ static void write_note_to_worktree(const struct object_id *obj,
 {
 	enum object_type type;
 	unsigned long size;
-	void *buf = repo_read_object_file(the_repository, note, &type, &size);
+	void *buf = odb_read_object(the_repository->objects, note, &type, &size);
 
 	if (!buf)
 		die("cannot read note %s for object %s",