Alter calculator disabled by Group permissions

Problem/Motivation

You can't alter the calculated items when using group_permissions.

Steps to reproduce

See the class GroupPermissionsChainPermissionCalculator, as defined in group_permissions.services.yml, it overrides the ChainPermissionCalculator::calculatePermissions function from the flexible_permission module.

But when you go in the flexible_permission module, in the class ChainPermissionCalculator class, you see that the calculatePermissions function allow you to override calculated items by using PermissionCalculatorAlterInterface or PermissionCalculatorAlterInterfaceV2 on line 153.

      // Alter mode, allow all calculators to alter the complete build.
      $calculated_permissions->disableBuildMode();
      foreach ($this->getCalculators() as $calculator) {
        if ($calculator instanceof PermissionCalculatorAlterInterfaceV2) {
          $calculator->alterPermissions($account, $scope, $calculated_permissions);
        }
        elseif ($calculator instanceof PermissionCalculatorAlterInterface) {
          $calculator->alterPermissions($calculated_permissions);
        }
      }

But group_permissions didn't implement this code and so remove this functionnality.

Proposed resolution

Set the code above on line 72 of GroupPermissionsChainPermissionCalculator.php in order to retrieve this functionnality.