[12.x] Drupal 12.0 (and 11.5) beta targets

The following issues should be committed between 12.0.0-beta1 and 12.0.0-rc1 (ideally before 12.0.0-beta2).

• #3425412: [Oct 2026] Bump PHPStan rule level to 3
• Ensure that cspell: ignore lines are correct. See script in #3560682: Remove words not needed in cspell:ignore.
• #3278431: [Oct 2026] Use PHP 8 constructor property promotion for existing code (After PHPStan level 3)