public function enable($config, $app)
　↓
public function enable(array $meta, ContainerInterface $container)

    // プラグイン有効時
    public function enable($config, $app)
    {
        // リソースのコピー
        $file = new Filesystem();
        $file->mkdir($app['config']['plugin_html_realdir'] . '/samplepage/save_image', 0775);
        $to_path = $app['config']['plugin_html_realdir'] . '/samplepage/assets';
        $file->mirror(__DIR__.'/Resource/assets', $to_path);

        // jbimagesの画像保存先パスを置換
        $file_path = $to_path . '/js/vendor/tinymce/plugins/jbimages/config.php';
        $configs = file_get_contents($file_path);
        $search = '$config[\'img_path\'] = \'/plugin/samplepage/save_image\';';
        $replace = '$config[\'img_path\'] = \'' . $app['config']['plugin_urlpath'] . '/samplepage/save_image\';';
        $configs = str_replace($search, $replace, $configs);
        file_put_contents($file_path, $configs);

        // ブロックのコピー
        $this->copyBlock($app);
    }

    /**
     * ブロックファイルをブロックディレクトリにコピーしてDBに登録
     *
     * @param $app
     * @throws \Exception
     */
    private function copyBlock($app)
    {
        $file = new Filesystem();
        if (!$file->exists(sprintf("%s/%s.twig", $app['config']['block_realdir'], self::BLOCKFILENAME))) {
            $file->copy($this->Block, sprintf("%s/%s.twig", $app['config']['block_realdir'], self::BLOCKFILENAME));
            $app['orm.em']->getConnection()->beginTransaction();
            try {
                // ブロックの登録
                $Block = $this->registerBlock($app);
                // BlockPositionの登録
                $this->registerBlockPosition($app, $Block);
                $app['orm.em']->getConnection()->commit();
            } catch (\Exception $e) {
                $app['orm.em']->getConnection()->rollback();
                throw $e;
            }
        }
    }

    /**
     * ブロックの登録
     *
     * @return \Eccube\Entity\Block
     */
    private function registerBlock($app)
    {
        $DeviceType = $app['eccube.repository.master.device_type']->find(DeviceType::DEVICE_TYPE_PC);
        /** @var \Eccube\Entity\Block $Block */
        $Block = $app['eccube.repository.block']->findOrCreate(null, $DeviceType);
        $Block->setName(self::BLOCKNAME);
        $Block->setFileName(self::BLOCKFILENAME);
        $Block->setDeletableFlg(Constant::DISABLED);
        $Block->setLogicFlg(1);
        $app['orm.em']->persist($Block);
        $app['orm.em']->flush($Block);
        return $Block;
    }

    /**
     * BlockPositionの登録
     *
     * @param $Block
     */
    private function registerBlockPosition($app, $Block)
    {
        $blockPos = $app['orm.em']->getRepository('Eccube\Entity\BlockPosition')->findOneBy(
            array('page_id' => 1, 'target_id' => PageLayout::TARGET_ID_UNUSED),
            array('block_row' => 'DESC'));
        $BlockPosition = new BlockPosition();
        // ブロックの順序を変更
        if ($blockPos) {
            $blockRow = $blockPos->getBlockRow() + 1;
            $BlockPosition->setBlockRow($blockRow);
        } else {
            // 1番目にセット
            $BlockPosition->setBlockRow(1);
        }
        $PageLayout = $app['eccube.repository.page_layout']->find(1);
        $BlockPosition->setPageLayout($PageLayout);
        $BlockPosition->setPageId($PageLayout->getId());
        $BlockPosition->setTargetId(PageLayout::TARGET_ID_UNUSED);
        $BlockPosition->setBlock($Block);
        $BlockPosition->setBlockId($Block->getId());
        $BlockPosition->setAnywhere(Constant::DISABLED);
        $app['orm.em']->persist($BlockPosition);
        $app['orm.em']->flush($BlockPosition);
    }

$Block = $container->get(\Eccube\Repository\BlockRepository::class)->findOneBy(array('file_name' => self::BLOCKFILENAME));
$Block = $container->get(\Eccube\Repository\BlockRepository::class)->newBlock($DeviceType);
$em->persist($Block);

    /**
     * リソースファイル等をコピー
     * コピー元となるファイルの置き場所は固定であり、
     * [プラグインコード]/Resource/assets
     * 配下に置かれているファイルが所定の位置へコピーされる
     *
     * @param $pluginCode
     */
    public function copyAssets($pluginCode)
    {
        $assetsDir = $this->calcPluginDir($pluginCode).'/Resource/assets';

        // プラグインにリソースファイルがあれば所定の位置へコピー
        if (file_exists($assetsDir)) {
            $file = new Filesystem();
            $file->mirror($assetsDir, $this->eccubeConfig['plugin_html_realdir'].$pluginCode.'/assets');
        }
    }

<link rel="stylesheet" href="{{ asset('assets/css/fileupload/jquery.fileupload.css', 'admin') }}">

<link rel="stylesheet" href="{{ asset('tbsCustom/assets/css/fileupload/jquery.fileupload.css', 'plugin') }}">

{{ asset('tbsCustom/save_image/', 'plugin') }}

$eccubeConfig['eccube_html_plugin_dir']

/** @var \Symfony\Component\Asset\Packages $manager */
$manager = $container->get('assets.packages');
$path = $manager->getUrl('tbsCustom/save_image', 'plugin')