support shiftKeyboardStep from numberControl, cleanup "attemped*Emitter" in AccessibleValueHandler, https://github.com/phetsims/scenery-phet/issues/528
support shiftKeyboardStep from numberControl, cleanup "attemped*Emitter" in AccessibleValueHandler, https://github.com/phetsims/scenery-phet/issues/528

phetsims/sun,phetsims/sun,phetsims/sun