Widgets: Perform 'widgets_admin_page' action in block widget editor

Perform the 'widgets_admin_page' action just prior to outputting markup for the
widgets block editor so as to maximise backwards compatibility with the old
screen.

Follows [51037].
See #51506.
Props isabel_brison.

Built from https://develop.svn.wordpress.org/trunk@51038


git-svn-id: http://core.svn.wordpress.org/trunk@50647 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/widgets-form-blocks.php

@@ -56,6 +56,13 @@ wp_enqueue_style( 'wp-edit-widgets' );
 do_action( 'enqueue_block_editor_assets' );
 
 require_once ABSPATH . 'wp-admin/admin-header.php';
+
+/**
+ * Fires before the Widgets administration page content loads.
+ *
+ * @since 3.0.0
+ */
+do_action( 'widgets_admin_page' );
 ?>
 
 <div id="widgets-editor" class="blocks-widgets-container"></div> 

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.8-alpha-51037';
+$wp_version = '5.8-alpha-51038';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.