add Refinement overload to findFirst

[wmaurer]

The Refinement findFirst overload would be useful when dealing with arrays of union types. Right now the workaround is to folllow a findFirst with a filter:

    pipe(
        ...,
        O.findFirst(Vehicle.is.Bicycle),
        O.filter(Vehicle.is.Bicycle),
        ...
    )

[gcanti]

Thanks @wmaurer, released.