Introduce Typed Class Constants and raise the bar to PHP >= 8.3.0

Problem/Motivation

Typed Class Constants are introduced in PHP 8.3.
PHP 8.3 is only supported as of Drupal 10.2, according to the Drupal PHP requirements →

Steps to reproduce

Proposed resolution

Remaining tasks

- release new stable release,
- wait some weeks for user base feedback
- re-apply the patch from #12
- amend file .info.yml with add core_version_requirement: ^8 || ^9 || ^10 || ^11 (Not, since this not precies enough)
- amend file composer.json with "require": "php>=8.3.0"
- release new stable release, supporting only PHP 8.3 and higher,

User interface changes

API changes

Data model changes