Convert radio form controls to TS

[ryankeairns]

Summary

Converts EuiRadio and EuiRadioGroup to TypeScript.

Note: I attempted to convert the docs example, however it's part of the long 'Form controls' page and I think it may necessitate a setup similar to EuiSelectable to handle the props and Options in the example. Those props pull from a types.tsx that lives with the src component code... I'm speaking out of my depth here, but there are many other form controls which have not been converted in this space and something tells me this may be some sort of solution that rolls these all together. Anyway, given that, I bailed on converting the docs example since this was only for the radio bits.

Checklist

• Checked in dark mode
• Checked in mobile
• Checked in IE11 and Firefox
• Props have proper autodocs
• Added documentation examples
• Added or updated jest tests
• Checked for breaking changes and labeled appropriately
• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[chandlerprall]

The old index.d.ts exported a number of values that index.ts does not. This creates a breaking change, and we should strive to export the meaningful types/interfaces.

Specifically these are now missing from the exports:

• EuiRadioGroupOption
• EuiRadioGroupChangeCallback
• EuiRadioGroupProps
• EuiRadioProps

[chandlerprall]

Anyway, given that, I bailed on converting the docs example since this was only for the radio bits.

I think that's the right call, for all the reasons you mentioned 👍

[chandlerprall]

Changes LGTM; pulled and built eui.d.ts locally, tested to ensure expected types are still exported from the @elastic/eui module

[thompsongl]

LGTM. Kibana type check passes with the generated d.ts