Get the post title.
The post title is fetched and if it is blank then a default string is returned.
wp-admin/includes/template.php, but we can't include that
- It causes bugs with test fixture generation and strange Docker 255 error codes.
- It's in the admin; ideally we shouldn't be including files from the admin for a block's output. It's a very small/simple function as well, so duplicating it isn't too terrible.