why does Checkbox need a separate listener for keyboard input?

[pixelzoom]

Noted while working on #488.

Checkbox has this code related to "firing" of its state change:

    // interactivity
    var fire = function() {
      if ( self.enabledProperty.value ) {
        var newValue = !property.value;
        toggledEmitter.emit( newValue );
      }
    };

    var checkboxButtonListener = new ButtonListener( {
      fire: fire
    } );
    this.addInputListener( checkboxButtonListener );

    // a11y - fire the listener when checkbox is clicked with keyboard or assistive technology
    var changeListener = {
      change: fire
    };
    this.addInputListener( changeListener );

Why do we need to add another listener for a11y that calls the exact same function as the ButtonListener that was already added? This should be handled by ButtonListener; it should be able to handle all types of button input, including keyboard/AT, not just pointer.

[pixelzoom]

Transferring this issue from scenery-phet to sun, since Checkbox lives in sun.

[jessegreenberg]

This listener was added before phetsims/scenery#888, but since that is done there is no need to have a separate listener for a11y.

Response to a11y input should probably be moved to ButtonListener, but I am going to review usages of ButtonListener to make sure.

[jessegreenberg]

ButtonListener was instrumented for a11y in #959, and this a11y listener was removed from Checkbox.

[jessegreenberg]

Closing since the listener was removed from Checkbox.