REST API: Fix links format in OPTIONS requests for non-variable routes.

Props nsundberg, johnwatkins0, birgire.
Fixes #49149.

Built from https://develop.svn.wordpress.org/trunk@47326


git-svn-id: http://core.svn.wordpress.org/trunk@47120 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/class-wp-rest-server.php

@@ -1288,7 +1288,11 @@ class WP_REST_Server {
 			// For non-variable routes, generate links.
 			if ( strpos( $route, '{' ) === false ) {
 				$data['_links'] = array(
-					'self' => rest_url( $route ),
+					'self' => array(
+						array(
+							'href' => rest_url( $route ),
+						),
+					),
 				);
 			}
 		}