Add 'grid' layout support to RectangularRadioButtonGroup.

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RectangularRadioButtonGroup lacks support for grid layout of radio buttons, a layout that has been requested in several sims: Calculus Grapher, Vector Addition, Projectile Sampling Distributions, ... A grid layout must currently be faked (see example below) and an API that naturally supports grid layout would be a big improvement.

For example in calculus-grapher CurveManipulationTypeRadioButtonGroup:

To force the above grid layout required creative use of options, as shown below. Making this behave as desired was both difficult and brittle, easily broken by changes to the surround layout - see phetsims/calculus-grapher#401.

      // RectangularRadioButtonGroup does not support grid layout. These options are a bit of a hack to implement
      // a 2x2 grid. Values were set empirically to make the vertical and horizontal spacing look the same.
      // See https://github.com/phetsims/calculus-grapher/issues/351 and https://github.com/phetsims/calculus-grapher/issues/401.
      orientation: 'horizontal',
      preferredWidth: 155,
      widthSizable: false,
      justify: 'center',
      spacing: 5,
      wrap: true,
      lineSpacing: 5

[pixelzoom]

Duplicate of #513 which was requested in 5/2019.