Issue [#3252386]

This adds support for attributes in PHP 8.1 - i.e we need nested attrbiutes.

core/lib/Drupal/Component/Plugin/Attribute/AttributeBase.php

+<?php
+
+namespace Drupal\Component\Plugin\Attribute;
+
+/**
+ * Provides a base class for classed attributes.
+ */
+abstract class AttributeBase implements AttributeInterface {
+
+  /**
+   * The class used for this attribute class.
+   */
+  protected string $class;
+
+  /**
+   * The provider of the attribute class.
+   */
+  protected string|null $provider = NULL;
+
+  /**
+   * @param string $id
+   *   The attribute class ID.
+   */
+  public function __construct(
+    protected readonly string $id
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getProvider(): ?string {
+    return $this->provider;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setProvider(string $provider): void {
+    $this->provider = $provider;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getId(): string {
+    return $this->id;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getClass(): string {
+    return $this->class;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setClass(string $class): void {
+    $this->class = $class;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function get(): array|object {
+    return array_filter(get_object_vars($this) + [
+      'class' => $this->getClass(),
+      'provider' => $this->getProvider(),
+    ], function ($value, $key) {
+      return !($value === NULL && ($key === 'deriver' || $key === 'provider'));
+    }, ARRAY_FILTER_USE_BOTH);
+  }
+
+}