Support {@inheritdoc}

On
#1906474: [policy adopted] Stop documenting methods with "Overrides …"
the Drupal Core community adopted a standard for documentation blocks on class methods that look like this:

  /**
   * {@inheritdoc}
   */
  public function getValue() {
    return $this->value;
  }

The API module should basically detect a doc block containing nothing but {@inheritdoc} and treat it the same as a nonexistent doc block, which will then mean the method inherits docs from the parent method.