Switch Component Improvements

[lychyi]

🚀 Feature Proposal

After doing a thorough test re-write (#386) of Switch, there are some improvements we can make to this component.

• I don't think we need to specify tabIndex={0}, this is the default already.
• We should map a static member Switch.ErrorType.Alert to ErrorType from canvas-kit-react-common. It's kind of a pain to import that also just to use Switch.
• Per some conversations that @NicholasBoll had with a11y in the past, we should probably make the role attribute a configurable prop. Instead of checkbox it could be something like switch.
• We should probably rename the elements SwitchBackground and SwitchCircle to something more semantically correct like SwitchTrack and SwitchThumb.

Motivation

Our components can always be a bit better 🌞