totally reworked grabButtonNode (draggable as child of button), https://github.com/phetsims/scenery-phet/issues/421
totally reworked grabButtonNode (draggable as child of button), https://github.com/phetsims/scenery-phet/issues/421

phetsims/scenery-phet,phetsims/scenery-phet,phetsims/scenery-phet