MC-15763: Introduce critical CSS scope loaded through head

- Stabilization

Author: vzabaznov

app/code/Magento/Theme/Controller/Result/AsyncCssPlugin.php

@@ -58,7 +58,9 @@ function ($matches) use (&$cssMatches) {
                     }
                     $media = $media ?? 'all';
                     $loadCssAsync = sprintf(
-                        '<link rel="preload" as="style" media="%s" href="%s">',
+                        '<link rel="preload" as="style" media="%s" .
+                         onload="this.onload=null;this.rel=\'stylesheet\'"' .
+                        'href="%s">',
                         $media,
                         $href
                     );