[proposal] introduce design tokens

[DRiFTy17]

Proposal

This is a 2-step process. We should start by exposing all of our design tokens for all colors, states... etc. (much like open props
and tailwind) whether the Forge components make use of them or not. This would be in the form of CSS custom properties and
Sass variables. Currently, all of the token values live directly in the library, so part 1 is fairly simple.

The second part of this is to consume these tokens at build time within Forge from an external source of truth so that design tokens are managed by UX teams and automatically pull into Forge. This would likely be in the form of an npm package with typings, but is essentially a JSON file.

Affected components

All components that provide visual styles. These components would now import the values from the design tokens instead of importing them from within the library itself.

Benefits

• Lifts the design token values out of the library for use maintaining and using elsewhere
• Enables designers to maintain the look-and-feel more easily

Caveats

None that I can think of.