Second take at cycling three-state filled-in checkboxes

[hartwork]

Hi!

When I opened #3875 over three years ago, I knew a lot less about indeterminate checkboxes. Since then, I have researched indeterminate checkboxes more and have implemented a cycling tristate checkbox as a Vue.js component that supports form submission and makes use of checkboxes native to the browser. So I may be able to solve the same problem for Materialize myself by now… and I still need tristate checkboxes to support "maybe" for an answer in my mini-Doodle jawanndenn, if I don't want jawanndenn to say goodbye to Materialize for that single feature.

Is fully-functional cycling tri-state checkboxes that match Materialize something you want to have solved inside or outside of Materialize in 2020?

Simplified, it would take:

• a new filled-in indeterminate graphic similar to the one seen at https://www.materialui.co/icon/indeterminate-check-box and
• adjusting the current checkbox JS to
  • cycle though all three states and
  • send value indeterminate rather than on during form submission.

What do you think?

Best, Sebastian