Fix for MdRadioGroup absolute positioning

[kajsaeggum]

Describe your changes

The individual radio inputs of MdRadioGroup are absolutely positioned, without having a parent element within the component as relatively positioned. This resulted in weird positioning behaviour in a real life application since the position then became relative to an element further up the DOM, outside of the MdRadioGroup component itself.

Also used option.id when concatenating the options id-prop, instead of option.text which is more likely to be something more than plain text or number. (In my case the option.text-prop was a ReactNode/JSX element, which resulted in an id that looked like radio_customGroupName_[object: Object]

Checklist before requesting a review

• I have performed a self-review and test of my code
• If new component: Is story for component created in stories-folder?
• If new component: Is tsx-file import added to packages/react/index.tsx?
• If new component: Is css-file added to packages/css/index.css?