Add support for yearAndMonth mode

[oliveryasuna]

iOS now supports a year/month picker natively.

if #available(iOS 17.4, *) {
    picker.datePickerMode = .yearAndMonth
} else {
    picker.datePickerMode = .date
    // Technically, iOS did support it, but it had to be set like this.
    picker.datePickerMode = .init(rawValue: 4269) ?? .date
}

if #available(iOS 13.4, *) {
    picker.preferredDatePickerStyle = .wheels
}

[oliveryasuna]

I opened a PR for this: #89