Refactor theme and sprinkles

[veej]

This PR is a first step towards the rationalization of design tokens and sprinkles. It introduces the following changes:

• The spacing scale is no longer exposed as design tokens (theme), but only as sprinkles (atoms). We added a few more steps, like 16, 120, 160
• The available border radiuses are no longer exposed as design tokens. borderRadius now accepts every step of the spacing scale
• boxShadows are no longer exposed as design tokens. They're instead inferred from outline colors, providing 3 different boxShadow configs (regular, bottom only and strong) for each outline color. Only the 3 elevations are kept in the theme as design tokens.
• 2 more dataViz palettes have been added (pastel, dark)
• The typography tokens have been refactored to allow to specify:
  • a font family for each typography family
  • a font weight for each typography family/size combination + an additional "strong" weight for each body size
  • a letter spacing for each family/size combination