function getInitialState(props) {
  const activeIndex = getInitialValue(props, 'activeIndex')
  const selectedItems = getInitialValue(props, 'selectedItems')

  return {
    activeIndex,
    selectedItems,
  }
}
Gets the initial state based on the provided props. It uses initial, default
and controlled props related to state in order to compute the initial value.

@param {Object} props Props passed to the hook.
@returns {Object} The initial state.