[10.x] Add 'hashed' cast

[gdebrauwer]

The encrypted cast exists, but a cast that hashes a value does not exist yet. In a lot of applications (even Laravel's default application), the user model has a password. I think it makes sense to have a hashed cast that ensures the password (or some other attribute's value) is always hashed before being saved in the database.

Example:

public $casts = [
    'password' => 'hashed',
];