Constructive dismissal isn’t illegal, it merely allows the employees to receive benefits and make claims as though they had been dismissed. California is an at-will employment state, so unless these employees have contracts stating otherwise (including the employee handbook, unless it has verbiage stating it is not legally binding), their dismissal is legal.
Apple is giving each employee who chooses to resign a $12.5k severance package. Assuming Apple doesn’t plan on fighting any unemployment claims made by these employees, what else you think they would be able to get after a successful lawsuit?