REST API: Allow fetching multiple terms at once via the slug parameter.

This matches a similar change previously made for posts (#38579) and an upcoming change for users (#40213).

Props wonderboymusic, MatheusGimenez, curdin.
Fixes #40027.


git-svn-id: https://develop.svn.wordpress.org/trunk@40376 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-terms-controller.php

@@ -978,7 +978,10 @@ class WP_REST_Terms_Controller extends WP_REST_Controller {
 
 		$query_params['slug'] = array(
 			'description'       => __( 'Limit result set to terms with a specific slug.' ),
-			'type'              => 'string',
+			'type'              => 'array',
+			'items'             => array(
+				'type'          => 'string'
+			),
 		);
 
 		/**