Update Pajamas UI kit (Figma) to use design tokens

⚠️ This issue represents our plans assuming we're able to successfully build a Figma plugin to sync our design tokens from gitlab-ui into Figma. If we're unable to do so, our approach here will change.

Tasks

• Variables file (published) containing:
  • All colors tokenized (styles still available)
  • Global semantic color tokens (surface, text)
  • Component semantic color tokens (design decisions, states)

Unanswered questions

• Dropshadow color takes a single variable that encompass the RGB hex and an alpha value. Extra transformation/handling might be needed to solve this.