Added Plugin::getTypeFromManager() with tests.

Closes #3414461

src/Plugin.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\helper;
 
+use Drupal\Component\DependencyInjection\ReverseContainer;
 use Drupal\Component\Plugin\CategorizingPluginManagerInterface;
 use Drupal\Component\Plugin\FallbackPluginManagerInterface;
 use Drupal\Component\Plugin\PluginManagerInterface;
@@ -36,6 +37,22 @@ class Plugin {
     return $plugin_manager;
   }
 
+  /**
+   * Get the plugin type from a plugin manager object.
+   *
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
+   *   The plugin manager.
+   *
+   * @return string|null
+   *   The plugin type if found, otherwise NULL.
+   */
+  public static function getTypeFromManager(PluginManagerInterface $manager): ?string {
+    $service_id = \Drupal::service(ReverseContainer::class)->getId($manager);
+    if ($service_id && str_starts_with($service_id, 'plugin.manager.')) {
+      return str_replace('plugin.manager.', '', $service_id);
+    }
+  }
+
   /**
    * Call a plugin callback and return its result.
    *