Editor: fix classname output on blocks without layout.

Prevents layout classnames from being output on blocks with no layout support and no child layout classnames by returning early from `wp_render_layout_support_flag`.

Props andrewserong.
Fixes #60292.

Built from https://develop.svn.wordpress.org/trunk@57328


git-svn-id: http://core.svn.wordpress.org/trunk@56834 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-supports/layout.php

@@ -615,6 +615,9 @@ function wp_render_layout_support_flag( $block_content, $block ) {
 			$processor->add_class( $class_name );
 		}
 		return $processor->get_updated_html();
+	} elseif ( ! $block_supports_layout ) {
+		// Ensure layout classnames are not injected if there is no layout support.
+		return $block_content;
 	}
 
 	$global_settings = wp_get_global_settings();