message: chore(devenv): fix theme switcher being reset
  This change fixes theme switcher selection being reset when user clicks
  on another Storybook add-on tab and then goes back to Carbon theme
  add-on tab.
diff: -import React, { useCallback } from 'react';
  +import React, { useCallback, useState } from 'react';
  import PropTypes from 'prop-types';
  import { Form } from '@storybook/components';
  import { CURRENT_THEME } from '../shared';
  @@ -7,9 +7,12 @@ import { CURRENT_THEME } from '../shared';
  * Storybook add-on panel for Carbon theme switcher.
  */
  const Panel = ({ api, active }) => {
  + const [currentTheme, setCurrentTheme] = useState('white');
  const handleChange = useCallback(
  event => {
  - api.getChannel().emit(CURRENT_THEME, event.target.value);
  + const { value } = event.target;
  + setCurrentTheme(value);
  + api.getChannel().emit(CURRENT_THEME, value);
  },
  [api]
  );
  @@ -17,7 +20,7 @@ const Panel = ({ api, active }) => {
  active && (
  <Form>
  <Form.Field label="Select Carbon theme:">
  - <Form.Select initialValue="white" name="carbon-theme" onChange={handleChange} size="flex">
  + <Form.Select name="carbon-theme" value={currentTheme} onChange={handleChange} size="flex">
  <option key="white" value="white">
  white
  </option>
  