[2.0.0-beta2] Drag & drop support in layout builder

Are we sure this wrapper is added only in Layout Builder preview and not elsewhere?

I will try with UI Styles Layout Builder, but I think this wrapper is needed everywhere as soon as the component is used as a layout.

I can't test with UI Styles until 🐛 Type error with callback Active is fixed.

Proposal:

--- a/modules/ui_patterns_layouts/src/Element/ComponentAlterer.php
+++ b/modules/ui_patterns_layouts/src/Element/ComponentAlterer.php
@@ -39,8 +39,14 @@ class ComponentAlterer implements TrustedCallbackInterface {
       foreach (Element::children($element[$region_id]) as $block_id) {
         $element["#slots"][$region_id][$block_id] = $element[$region_id][$block_id];
       }
-      if (isset($element[$region_id]['#attributes'])) {
+      if (isset($element[$region_id]['#attributes']) && isset($element["#slots"][$region_id])) {
         $element['#region_attributes'][$region_id] = new Attribute($element[$region_id]['#attributes']);
+        $element["#slots"][$region_id] = [
+          "#type" => "html_tag",
+          "#tag" => "div",
+          "#attributes" => $element[$region_id]['#attributes'],
+          "content" => $element["#slots"][$region_id],
+        ];
       }
       unset($element[$region_id]);
     }