feat: Update CustomProperties component to use JSON tokens

[aaronccasanova]

WHAT is this pull request doing?

This PR updates the CustomProperty component to use the recently added JSON tokens.

• Deleted TypeScript design token objects
• Replaced tokens directory with a single tokens.ts
  (This simplifies the implementation while still maintaining an opinion on the structure of the tokens object and how it's consumed in TypeScript files)
• Updated tokens.ts to import the JSON token files

How to 🎩

🖥 Local development instructions
🗒 General tophatting guidelines
📄 Changelog guidelines

Copy-paste this code in playground/Playground.tsx:

import React from 'react';
import {Page} from '../src';

export function Playground() {
  return (
    <Page title="Playground">
      {/* Add the code you want to test in here */}
    </Page>
  );
}

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide
• For visual design changes, ping @ sarahill to update the Polaris UI kit

[BPScott]

https://github.com/Shopify/polaris-react/blob/main/loom.config.ts#L154 is a demo of adding additional rollup plugins. You'll need to add @rollup/plugin-json.

[kyledurand]

🤩

[kyledurand]

These links are temporary right? Not sure it's worth leaving as a comment. Easy enough just to copy and paste and add a few examples

[aaronccasanova]

In addition to the above screenshot, I verified in their GitHub API and FAQ wikis these are permalinks. I actually like having this reference as we can make sure the existing test cases still pass during future updates. That said, I'm also fine with removing the link as it's now checked into source control if we ever need it.