(tests will be updated when we have confirmed if the API changes are good to go)

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Related #4607

This PR adds support for 3 button modals according to the latest modal spec. Since our existing Modal API expects only 1 primary and 1 secondary button, a secondaryButtons prop is introduced which can be used in place of the secondaryButtonText and onSecondarySubmit props. The secondaryButtons prop expects an array of up to 2 objects with the following shape:

{
  buttonText: PropTypes.string,
  onClick: PropTypes.func,
}

if an onClick handler is not supplied to the secondary buttons in a ComposedModal it will fall back to the internal handleRequestClose method by default

Changelog

New

• secondaryButtons prop
• 3 button modal styles (not including linear directional modals)

Testing / Reviewing

Confirm the 3 button modal styles appear correct and there are no visual regressions with existing supported modal styles