add "show ring" light block (from pxt-adafruit)

[ktdreyer]

Is your feature request related to a problem? Please describe.
https://github.com/microsoft/pxt-adafruit has a very cool "show ring" light block that is simple for my kids to point and click on each individual light bulb and choose the color for each one. You can see some kids demoing this feature at https://youtu.be/Q_wt7VoApFY?t=635

Describe the solution you'd like
Please consider porting this "show ring" light option to pxt-maker.

Describe alternatives you've considered

• pxt-maker has a "set all pixels to <color>" block that sets everything to one single color. This is not the same thing as pointing and choosing individual pixels.
• pxt-maker also has a "set pixel color at <int> to <color>" block that controls one single pixel. This is much more complicated and requires reading, counting, etc. instead of the simplicity of visually pointing and clicking. Kids have to understand the following: Which bulb is "0"? Why does it start at zero, and not at 1? If there's ten bulbs, why is the last one "nine"? Does the circle go clockwise or counter-clockwise? It's a lot to just to get started, and makes it difficult to play around quickly.

Additional context
Here's a screenshot of the block in pxt-adafruit. This UI is extremely intuitive to children who are doing their first lessons: