Add embed handling for block widgets in frontend (#26307)

* Add embed handling for block widgets

* Add comment explaining feature and implementation in core

* Add ticket ref

* full-stop

lib/class-wp-widget-block.php

@@ -54,7 +54,17 @@ public function __construct() {
 	 */
 	public function widget( $args, $instance ) {
 		echo $args['before_widget'];
-		echo do_blocks( $instance['content'] );
+		$content = do_blocks( $instance['content'] );
+
+		// Handle embeds for block widgets.
+		//
+		// When this feature is added to core it may need to be implemented
+		// differently. WP_Widget_Text is a good reference, that applies a
+		// filter for its content, which WP_Embed uses in its constructor.
+		// See https://core.trac.wordpress.org/ticket/51566.
+		global $wp_embed;
+		echo $wp_embed->autoembed( $content );
+
 		echo $args['after_widget'];
 	}