How to map Binding with optional value in SwiftUI

Issue #838

We can write our custom Binding

import SwiftUI

extension Binding where Value == Date? {
    func flatten(defaultValue: Date) -> Binding<Date> {
        Binding<Date>(
            get: { wrappedValue ?? defaultValue },
            set: {
                wrappedValue = $0
            }
        )
    }
}

Then use in places where it needs Binding with non-optional value

DatePicker(
    "",
    selection: $date.flatten(defaultValue: Date()),
    displayedComponents: .hourAndMinute
)
.datePickerStyle(WheelDatePickerStyle())