[Spinner] Default button not activated on ENTER

This is analogue to JDK-8096725 (was fixed for ComboBox and DatePicker), just for Spinner and only for ENTER (ESC is working as expected, at least in regard to the cancel button)

To reproduce, take the example from that bug, add an editable spinner:

// JW: added spinner
Spinner<Integer> spinner = new Spinner<>(0, 200, 20);
spinner.setEditable(true);
...
vbox.getChildren().add(spinner);

then run,
- edit spinner
- press enter
- expected: okay button activated, that is OK printed
- actual: nothing happens