Resolve #3420984 "Convert layout displayvariant"

Closes #3420984

core/lib/Drupal/Core/Display/Attribute/DisplayVariant.php

+<?php
+
+namespace Drupal\Core\Display\Attribute;
+
+use Drupal\Component\Plugin\Attribute\Plugin;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Defines a display variant attribute object.
+ *
+ * Display variants are used to dictate the output of a given Display, which
+ * can be used to control the output of many parts of Drupal.
+ *
+ * Variants are usually chosen by some selection criteria, and are instantiated
+ * directly. Each variant must define its own approach to rendering, and can
+ * either load its own data or be injected with data from another Display
+ * object.
+ *
+ * Plugin namespace: Plugin\DisplayVariant
+ *
+ * For working examples, see
+ * - \Drupal\Core\Render\Plugin\DisplayVariant\SimplePageVariant
+ * - \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
+ *
+ * @see \Drupal\Core\Display\VariantInterface
+ * @see \Drupal\Core\Display\VariantBase
+ * @see \Drupal\Core\Display\VariantManager
+ * @see \Drupal\Core\Display\PageVariantInterface
+ * @see plugin_api
+ */
+#[\Attribute(\Attribute::TARGET_CLASS)]
+class DisplayVariant extends Plugin {
+
+  /**
+   * Constructs a DisplayVariant plugin attribute object.
+   *
+   * @param string $id
+   *   The plugin ID.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup $admin_label
+   *   The administrative label.
+   * @param class-string|null $deriver
+   *   (optional) The deriver class.
+   */
+  public function __construct(
+    public readonly string $id,
+    public readonly TranslatableMarkup $admin_label,
+    public readonly ?string $deriver = NULL
+  ) {}
+
+}