Switch a11y tweaks

[giuseppeg]

During the workshop I noticed that you were using a combo of input + button in the Switch component to toggle state. This PR is a small refactoring to make it accessible to screen readers. In the original version I found the following issues:

• The input was display: none so it is not focusable and screen readers couldn't read it. I made it visually hidden (see the css file).
• The button has a different semantic meaning therefore when changing value (by clicking the btn) the screen reader would not announce the new state. With a checkbox that happens by default.
• Since the checkbox in my version is the main player now we can assert against its checked state, that's why I had to tweak the test utils/extension.
• The input was just used for its native switch nature (checked/unchecked) to update the Switch state, but it was controlled by a button - better use a label for that.

✌️☮️

[codecov[bot]]

Codecov Report

Merging #24 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #24   +/-   ##
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  Coverage    41.6%   41.6%           
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  Files          21      21           
  Lines         411     411           
  Branches       62      62           
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  Hits          171     171           
  Misses        201     201           
  Partials       39      39

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