Address TODO about propagating options to button model.

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This NOTE was added by @jonathanolson when he converted RectangularPushButton to TypeScript. It should have been a TODO, with an issue. The same problem needs to be addressed in RoundPushButton, and any other sun button that propagates all of its options to its model class. It's unlikely that there's a TODO in every location where this needs to be addressed.

// NOTE: Let's not create PushButtonModel with these options?
export type RectangularPushButtonOptions = SelfOptions & RectangularButtonOptions & PushButtonModelOptions;