REST API: Add batch support for posts and terms controllers.

This also exposes the value of `allow_batch` in `OPTIONS` requests to a route.

A future commit will add batch support to more resources.

Props spacedmonkey, chrisvanpatten.
See #53063.


git-svn-id: https://develop.svn.wordpress.org/trunk@52068 602fd350-edb4-49c9-b593-d223f7449a82

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

@@ -24,6 +24,14 @@ class WP_REST_Widgets_Controller extends WP_REST_Controller {
 	 */
 	protected $widgets_retrieved = false;
 
+	/**
+	 * Whether the controller supports batching.
+	 *
+	 * @since 5.9.0
+	 * @var array
+	 */
+	protected $allow_batch = array( 'v1' => true );
+
 	/**
 	 * Widgets controller constructor.
 	 *
@@ -56,7 +64,7 @@ class WP_REST_Widgets_Controller extends WP_REST_Controller {
 					'permission_callback' => array( $this, 'create_item_permissions_check' ),
 					'args'                => $this->get_endpoint_args_for_item_schema(),
 				),
-				'allow_batch' => array( 'v1' => true ),
+				'allow_batch' => $this->allow_batch,
 				'schema'      => array( $this, 'get_public_item_schema' ),
 			)
 		);
@@ -90,7 +98,7 @@ class WP_REST_Widgets_Controller extends WP_REST_Controller {
 						),
 					),
 				),
-				'allow_batch' => array( 'v1' => true ),
+				'allow_batch' => $this->allow_batch,
 				'schema'      => array( $this, 'get_public_item_schema' ),
 			)
 		);