feat: global-tokens-update

[zetareticoli]

As we started documenting border size and radius foundations on Design system style guide, I proceeded adding missing tokens to our list.

Added

• border size tokens
• new spacing size variants

Changed

• spacing variables are now explicit, not calculated
• spacing variants names, from scale to modifiers

Remove

• font-style tokens
• baseline variable

[zetareticoli]

@Fupete and @astagi please, let's check this PR so we can proceed with the merge.

I'll wait for the next alpha.15 to officially release the update.