Date validator #92

A date validator to which we give a DateAdapter and that validate that whatever we give is either a valid string representation of a date, or a Date. So basically forwarding to DateAdapter.isValid.

It should be used used pretty much for every datepicker in all our projects.

Usage is something like:

constructor(
    dateAdapter: DateAdapter,
) {
    const formControl = new FormControl(null, [date(dateAdapter)]);
}