[Draft/Proposal] Add state to Custom JS

[aparlato]

Description

Adds state concept to checkboxes. Debating whether this is overly complex and if not, whether we should extend it to the dropdown options. Offhand my thinking is: dropdowns seem more like an or scenario whereas checkboxes are more of an and scenario so dropdowns shouldn't need state in this way.

Closes # (downstream)

Solves the problem of needing to track state for a given style. Let me know when you want to review and I can provide an example config since this functionality is fairly complicated. That said, we might be able to build state into the functions in the config, but I've had many failed attempts there.

QA steps

• Ask @aparlato for a test config
• See if the state behavior feels appropriate
  • Doesn't set styling on other maps when the same map is in two panels
  • Doesn't mix up checkboxes and actual state of the map
  • Resets everything on style change

Author checklist

Create the PR

• Fill out PR template
• Make sure you've added a CHANGELOG entry under "Unreleased"
• Request a review
• Make any requested changes and get approval

After approval

• Merge any changes from main into your branch, resolve any conflicts
• Squash & merge changes into main
• Delete branch

[aparlato]

Closing this as excessive for our use case and not widely applicable. Downstream solved by #245 instead.