[4.1] PHP8 Support

[nanasess]

概要(Overview・Refs Issue)

• closes PHP8 Support #4579
• PHP8 対応

方針(Policy)

• PHP8 で動作するよう修正する

実装に関する補足(Appendix)

• Doctrine ORM 2.8.x にアップグレードしたのに伴い、以下の修正が必要
  • doctrine/persistence 2.0.x 対応(namespace 変更)
  • doctrine/migrations 2.3.x 対応(実装の変更)
  • Doctrine EventSubscriber の修正(namespace 変更)
• Mock を使用したテストケースがエラーになる
• MySQL のユニットテストが PDOException: SQLSTATE[42000]: Syntax error or access violation: 1305 SAVEPOINT DOCTRINE2_SAVEPOINT_3 does not exist でエラーになる
• プラグインインストール時、composer.json の config.platform が書き変わるため以下のようなエラーが発生する

  Problem 1
   - Root composer.json requires php ^7.3 but your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 2
   - doctrine/doctrine-cache-bundle is locked to version 1.4.0 and an update of this package was not requested.
   - doctrine/doctrine-cache-bundle 1.4.0 requires php ^7.1 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 3
   - doctrine/doctrine-migrations-bundle is locked to version 2.2.1 and an update of this package was not requested.
   - doctrine/doctrine-migrations-bundle 2.2.1 requires php ^7.1 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 4
   - doctrine/migrations is locked to version 2.3.0 and an update of this package was not requested.
   - doctrine/migrations 2.3.0 requires php ^7.1 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 5
   - friendsofphp/php-cs-fixer is locked to version v2.16.7 and an update of this package was not requested.
   - friendsofphp/php-cs-fixer v2.16.7 requires php ^7.1 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 6
   - setasign/fpdi is locked to version v2.3.4 and an update of this package was not requested.
   - setasign/fpdi v2.3.4 requires php ^5.6 || ^7.0 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 7
   - skorp/detect-incompatible-samesite-useragents is locked to version 1.0.0 and an update of this package was not requested.
   - skorp/detect-incompatible-samesite-useragents 1.0.0 requires php ^7.0 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 8
   - codeception/codeception is locked to version 2.4.5 and an update of this package was not requested.
   - codeception/codeception 2.4.5 requires php >=5.6.0 <8.0 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 9
   - dama/doctrine-test-bundle is locked to version v5.0.5 and an update of this package was not requested.
   - dama/doctrine-test-bundle v5.0.5 requires php ^7.1 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 10
   - fzaninotto/faker is locked to version v1.9.1 and an update of this package was not requested.
   - fzaninotto/faker v1.9.1 requires php ^5.3.3 || ^7.0 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 11
   - phpunit/phpunit is locked to version 6.5.14 and an update of this package was not requested.
   - phpunit/phpunit 6.5.14 requires php ^7.0 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
  Problem 12
   - doctrine/doctrine-migrations-bundle 2.2.1 requires php ^7.1 -> your php version (8.0.0; overridden via config.platform, same as actual) does not satisfy that requirement.
   - symfony/orm-pack v1.0.8 requires doctrine/doctrine-migrations-bundle * -> satisfiable by doctrine/doctrine-migrations-bundle[2.2.1].
   - symfony/orm-pack is locked to version v1.0.8 and an update of this package was not requested.
  

テスト（Test)

TODO

相談（Discussion）

• Doctrine DBAL 2.12.x にアップグレードしたのに伴い、システム要件が PHP7.3 or higer に変更となる

マイナーバージョン互換性保持のための制限事項チェックリスト

• 既存機能の仕様変更
• フックポイントの呼び出しタイミングの変更
• フックポイントのパラメータの削除・データ型の変更
• twigファイルに渡しているパラメータの削除・データ型の変更
• Serviceクラスの公開関数の、引数の削除・データ型の変更
• 入出力ファイル(CSVなど)のフォーマット変更

レビュワー確認項目

• 動作確認
• コードレビュー
• E2E/Unit テスト確認(テストの追加・変更が必要かどうか)
• 互換性が保持されているか
• セキュリティ上の問題がないか

[nanasess]

#4603 (comment)

互換性のなくなるいくつかの変更が必要なので、EC-CUBE4.1では互換性を優先し、PHP8対応は実施しません。
次のメジャーバージョンにてSymfony5対応と共にPHP8対応を検討します。

とのことですので、 本 PR は #4528 にマージして引き継ぎます。