REST API: Add support for "integer" type for meta and options

Previously Settings only supported "number" which meant it was possible to push floats to things like posts_per_page. This means now developers can also specify `type => ineger` in meta nad settings resgration.

Props flixos90.
Fixes #38393.

Built from https://develop.svn.wordpress.org/trunk@39058


git-svn-id: http://core.svn.wordpress.org/trunk@39000 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/rest-api/fields/class-wp-rest-meta-fields.php

@@ -404,6 +404,9 @@ abstract class WP_REST_Meta_Fields {
 			case 'string':
 				$value = (string) $value;
 				break;
+			case 'integer':
+				$value = (int) $value;
+				break;
 			case 'number':
 				$value = (float) $value;
 				break;