Issue #3492930: add xapi ActivityAnswer plugin.

src/Plugin/ActivityAnswer/Xapi.php

+<?php
+
+namespace Drupal\lms_xapi\Plugin\ActivityAnswer;
+
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\lms\Attribute\ActivityAnswer;
+use Drupal\lms\Entity\Answer;
+use Drupal\lms\Plugin\ActivityAnswer\ActivityAnswerBase;
+
+/**
+ * Xapi/TinCan activity plugin.
+ */
+#[ActivityAnswer(
+  id: 'xapi',
+  name: new TranslatableMarkup('Xapi / TinCan'),
+)]
+class Xapi extends ActivityAnswerBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getScore(Answer $answer): float {
+    $lrs_service = \Drupal::service('lms_xapi.tincan');
+    $account = $answer->getOwner();
+    $score = $lrs_service->getScoreFromLrs($answer->id(), 'lms_answer', $account->id());
+    return $score ?? 0;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function evaluatedOnSave(Answer $answer): bool {
+    return FALSE;
+  }
+
+
+}