[ChoiceList] Connecting the ChoiceList error the input with errors via describedByProp

[dleroux]

WHY are these changes introduced?

Fixes #1589

WHAT is this pull request doing?

1. add ariaDescribedBy prop to Checkbox and RadioButton
2. remove aria-describedby from the ChoiceList fieldset
3. updated the ChoiceDescriptor with a describedByError key to indicate whether to link the Error to the input or not.
4. added some tests

How to 🎩

Using the playground, ensure the radio buttons aria-describedby attribute matches the ID of the error field.

Copy-paste this code in playground/Playground.tsx:

import * as React from 'react';
import {Page, ChoiceList} from '../src';

interface State {}

export default class Playground extends React.Component<{}, State> {
  render() {
    return (
      <Page title="Playground">
        <ChoiceListExample />
      </Page>
    );
  }
}

class ChoiceListExample extends React.Component {
  state = {
    selected: ['hidden'],
  };

  render() {
    const {selected} = this.state;
    return (
      <ChoiceList
        title="Company name"
        choices={[
          {label: 'Hidden', value: 'hidden', describedByError: true},
          {label: 'Optional', value: 'optional'},
          {label: 'Required', value: 'required'},
        ]}
        selected={selected}
        onChange={this.handleChange}
        error="Company name cannot be hidden at this time"
      />
    );
  }

  handleChange = (value) => {
    this.setState({selected: value});
  };
}

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide

[dleroux]

If the type is boolean we don't want an area-describedby attribute

[dleroux]

The reason I went with describedByError: boolean as oppose to describedBy:string is because ChoiceList is the one generating the error and the id. So I thought to add describedByError to the descriptor was more clear. The choice has 1 error and this choice is described by that error.

[chloerice]

The API update makes sense to me, and the aria-describedby is now being set on the input as recommended 🚢