Add tokens to support HC mode in Design Tokens & Styles Library

[lboehling]

Initial token updates for HC theme have been made in a separate file (done so we could quickly iterate & test out the updates). Now that those tokens have been solidified more & are working in code, I think it's a good time to start adding them into our Design Tokens library so we can publish the border/color updates for HC theme in Figma together with the planned alpha release at the end of Q3.

TLDR: HC Tokens updates defined in HC Exploration Figma file should be copied over in the main design token library.

[lboehling]

tokens have been added! need a follow up design kit issue for applying the new border styles across several components