Add support for external design systems

[ingeniumed]

We will start with the Valet theme.json to create an enterprise Theme.json starter. We know that just the Theme.json is not perfect, but focusing on design tokens creates a project that we can deliver.

We will identify 20 (or so) tokens that need to be populated to create a visually different experience when applied to a theme (even something like 2023).

We will then look at extracting those tokens from the CDT's source code. This will likely require mapping or annotation to say X CSS Variable in the California Design System maps to Y custom property in Theme.json.

The final product will give us a few pieces:

• A new source for the design bridge tool: CSS variables.

• A v1 them.json for a Starter Enterprise Block Theme (aka Valet).

• A tool that we can use to quickly extract design language from a customer site and apply it to a demo site.