Migrate typography values to particles

[james-nash]

Is your feature request related to a problem? Please describe.
Currently, the SASS code in @buildit/gravity-ui-web defines a number of typography values that are used throughout the UI: Base font size, modular scale multipliers, default line-height, font family stack, etc.

They should be moved from there into this repo as design tokens. That way, we can begin to export and publish them into other formats to support platforms beyond just the web.

Describe the solution you'd like

• Add new typography design tokens in this repo
• Update the StyleDictionary config and scripts to export them as suitable SASS vars/maps/ whaetevr & TS vars (and anything else we migth support)
• Update the gravity-ui-web repo to:
  • Depend on the new version of @buildit/gravity-particles that contains the typography values
  • Update the SASS code so that it no longer contains its own typography variable declarations and instead imports them from @buildit/gravity-particles.