Add CheckboxRadio component

[skjnldsv]

• Uses the Material design icons
• Supports simple, sets and single-set checkboxes + radio (see docs)
• Supports indeterminate state
• Very straightforward! 🚀

A few examples:

[jancborchardt]

Wooooooah very nice! :) Sooo good to have this standardized.

Some design feedback:

• Each of the rows should be 44px height to conform to the min clickable/tappable area. The resulting whitespace will also look nice as separation.
• The radio set using checkmarks looks a bit off. Normally it’s a dot in a circle, like so https://material.io/develop/web/components/selection-controls/radio-buttons (and like we do currently already)
• What is the "Standard checkbox set" with a square inside the square? If that is the indeterminate setting – we should keep it how it looks like for us currently (with the dash/minus in there) since that is also kind of a standard: https://material.io/components/checkboxes#behavior

[jancborchardt]

Nice, works very well now, looks great and is accessible. 👍 design-wise!