Add aria-expanded attribute for accessibility

[jgrenat]

Hello !

As mentionned in #46, this PR adds the aria-expanded attribute :)

[luukdv]

Thanks!

The tests are a bit repetitive, can you change them to the following?

it(`has an expansion indicator (for accessibility) when toggled`, () => {
  render(<Hamburger toggled />)

  expect(screen.getByTestId('tilt')).toHaveAttribute('aria-expanded', 'true')
})

it(`doesn't have an expansion indicator (for accessibility) when closed`, () => {
  render(<Hamburger />)

  expect(screen.getByTestId('tilt')).toHaveAttribute('aria-expanded', 'false')
})

I'll define these attributes one level up and spread them into the individual components when I have time, so the repetition would be solved there as well.

[jgrenat]

Hello! Sure, I've updated the tests labels, let me know if you want me to change anything else 😀

[luukdv]

They're still a bit repetitive, can you change them (also the test contents) to the snippet above? So they'd be just 2 tests. Thanks in advance :)

[jgrenat]

Oh sorry, I missed that part, that's done now 😅