minor #1381 [Site] Load importmap polyfill conditionnaly (smnandre)

This PR was squashed before being merged into the 2.x branch.

Discussion
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[Site] Load importmap polyfill conditionnaly

With importmap support now over 90% of total usage.. i think we can try something here :)

Commits
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d322b5b [Site] Load importmap polyfill conditionnaly

Author: weaverryan

ux.symfony.com/config/packages/asset_mapper.yaml

@@ -6,6 +6,7 @@ framework:
         excluded_patterns:
             - '*/assets/styles/_*.scss'
             - '*/assets/styles/**/_*.scss'
+        importmap_polyfill: false
 
 react:
     controllers_path: '%kernel.project_dir%/assets/build/react/controllers'

ux.symfony.com/templates/base.html.twig

@@ -26,6 +26,14 @@
                 })();
             </script>
             {% block importmap %}
+                <script>
+                    if (!(HTMLScriptElement && HTMLScriptElement.supports?.('importmap'))) {
+                        document.head.appendChild(Object.assign(document.createElement("script"),{
+                            src:"https://cdn.jsdelivr.net/npm/[email protected]/dist/es-module-shims.min.js",
+                            async:true,
+                        }));
+                    }
+                </script>
                 {{ importmap('app') }}
             {% endblock %}
         {% endblock %}