docs(hooks): update widget hook xrefs to widgets-form

Update 5 cross-references for sidebar_admin_setup and
delete_widget from `wp-admin/widgets.php` to
`wp-admin/widgets-form.php` where the hooks now live.

Related to https://core.trac.wordpress.org/ticket/64224

Author: apermo

src/wp-admin/includes/ajax-actions.php

@@ -2382,7 +2382,7 @@ function wp_ajax_save_widget() {
 	 */
 	do_action( 'widgets.php' ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
 
-	/** This action is documented in wp-admin/widgets.php */
+	/** This action is documented in wp-admin/widgets-form.php */
 	do_action( 'sidebar_admin_setup' );
 
 	$id_base      = wp_unslash( $_POST['id_base'] );
@@ -2410,7 +2410,7 @@ function wp_ajax_save_widget() {
 			'delete_widget'      => '1',
 		);
 
-		/** This action is documented in wp-admin/widgets.php */
+		/** This action is documented in wp-admin/widgets-form.php */
 		do_action( 'delete_widget', $widget_id, $sidebar_id, $id_base );
 
 	} elseif ( $settings && preg_match( '/__i__|%i%/', key( $settings ) ) ) {
@@ -2486,7 +2486,7 @@ function wp_ajax_delete_inactive_widgets() {
 	do_action( 'load-widgets.php' ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
 	/** This action is documented in wp-admin/includes/ajax-actions.php */
 	do_action( 'widgets.php' ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
-	/** This action is documented in wp-admin/widgets.php */
+	/** This action is documented in wp-admin/widgets-form.php */
 	do_action( 'sidebar_admin_setup' );
 
 	$sidebars_widgets = wp_get_sidebars_widgets();

src/wp-includes/class-wp-customize-widgets.php

@@ -338,7 +338,7 @@ public function customize_controls_init() {
 		/** This action is documented in wp-admin/includes/ajax-actions.php */
 		do_action( 'widgets.php' ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
 
-		/** This action is documented in wp-admin/widgets.php */
+		/** This action is documented in wp-admin/widgets-form.php */
 		do_action( 'sidebar_admin_setup' );
 	}
 
@@ -1722,7 +1722,7 @@ public function wp_ajax_update_widget() {
 		/** This action is documented in wp-admin/includes/ajax-actions.php */
 		do_action( 'widgets.php' ); // phpcs:ignore WordPress.NamingConventions.ValidHookName.UseUnderscores
 
-		/** This action is documented in wp-admin/widgets.php */
+		/** This action is documented in wp-admin/widgets-form.php */
 		do_action( 'sidebar_admin_setup' );
 
 		$widget_id = $this->get_post_value( 'widget-id' );