Missing rest-api.php file affecting wp-settings.php

Our site has been down about a month. There’s an error message when someone attempts to load the page that is telling me the the wp-settings.php file is trying to find a file called rest-api.php in the wp_includes folder but there is no such file there. We’ve checked the WP theme and the plugins but they are all fine. We’re unsure what to do next. Does anyone know what a rest-api.php file is and how I can create one to upload to the wp_includes folder? Thanks!