Spinner missing a large size

[microbit-grace]

https://microbit-foundation.github.io/ui/?path=/story/feedback-spinner--sizes

There are only 2 sizes: "sm" and "md". Perhaps we should also show a large size?

[microbit-matt-hillsdon]

I think we have some much bigger ones somewhere — classroom? And maybe quite different. Might wait and see how this falls out after more app conversions.