Add type tokens for expressive reading experience

[shixiedesign]

Summary

"Carbon expressive theme" was originally conceived based on the assumption that majority of the experience on IBM.com is for long form reading and/or based on a marketing intent. This has proven to be not true over the last 2 years. We need productive experiences in the global masthead mega menu, IBM.com search, commerce, product configuration, search/filter on catalogs, and many more places. The common occurrence of productive experience (14px type size, and compact components such as tabs and checkboxes) too often for the approach of "expressive theme" to make sense.

The proposal is add a handful of tokens and expressive components to Carbon 10, and deprecate "expressive theme". Moving forward, Carbon for IBM.com would like to depend on Carbon core, and focus on delivering unique components that's needed by IBM.com on top of leveraging the full offering of Carbon Design System.

Add expressive type tokens

• Letter spacing unchanged: Letter-spacing: .16px

Token name	Value
caption-02	14px type size, 18px line height
label-02	14px type size, 18px line height
helper-text-02	14px type size, 18px line height

Additional notes

• Someone did complain about the 12px label a long time ago, and Mike was interested in a variant that allowed for 14 label, 14 form. Not sure if it ever went anywhere.
• This ask is not to update existing components with the new tokens. Just to add the new tokens.