Issue #3467759: [10.3] Convert VotingApiWidget plugins and discovery to attributes

Closes #3467759

src/Attribute/VotingApiWidget.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\votingapi_widgets\Attribute;
+
+use Drupal\Component\Plugin\Attribute\Plugin;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Defines a Voting API widget attribute object.
+ *
+ * Plugin Namespace: Plugin\votingapi_widgets.
+ *
+ * For a working example, see
+ * \Drupal\votingapi_widgets\Plugin\votingapi_widgets\UsefulWidget
+ *
+ * @see hook_vote_result_info_alter()
+ * @see \Drupal\votingapi_widgets\Plugin\VotingApiWidgetInterface
+ * @see \Drupal\votingapi_widgets\Plugin\VotingApiWidgetBase
+ * @see \Drupal\votingapi_widgets\Plugin\VotingApiWidgetManager
+ * @see plugin_api
+ */
+#[\Attribute(\Attribute::TARGET_CLASS)]
+class VotingApiWidget extends Plugin {
+
+  /**
+   * Constructs a VotingApiWidget attribute object.
+   *
+   * @param string $id
+   *   The plugin ID. The machine-name of the function plugin.
+   * @param \Drupal\Core\StringTranslation\TranslatableMarkup $label
+   *   The human-readable name of the widget.
+   * @param array $values
+   *   An array of possible vote values.
+   * @param class-string|null $deriver
+   *   (optional) The deriver class.
+   */
+  public function __construct(
+    public readonly string $id,
+    public readonly TranslatableMarkup $label,
+    public readonly array $values,
+    public readonly ?string $deriver = NULL,
+  ) {}
+
+}