Ensure core design tokens are documented with a description attribute as an example

[adamstankiewicz]

Part of the official W3C design token space being proposed is a description field to give a brief human-readable string to describe each token.

Given we have nearly 1500 tokens/variables, I believe asking to add description field to all of them in one go is a bit much and out of scope.

However, I would like for us to implement the description field on at least a subset of the more important tokens (e.g., global colors, spacing, and typography) to demonstrate the capabilities and show an example of the vision for all the tokens.

See https://design-tokens.github.io/community-group/format/#description fore more details.

[adamstankiewicz]

Maybe just colors and spacing 😄

[monteri]

#2112