feat: Add nav variant to Link component

[SirenaBorracha]

Summary

Add a nav option to the variant property to style the existing Link component with className usa-nav__link

Related Issues or PRs

#166

How To Test

yarn test

yarn storybook
Viewable from Typography > Link > Nav Link

Screenshots (optional)

Storybook

[haworku]

The way the classnames package works is it already conditionally includes the css. This means we don't need to add another ternary here. Check out the linked docs if you've never used this package before, its pretty convenient.

We should be able to get this still passing tests but following a pattern that's more similar to this pseudocodey example:

return unstyled?
    className // if its unstyled, only use classes passed in by props
     :  
   classnames( // otherwise use...
       'usa-link', // any classes required for component
       { 'random-class': true},  // and  any conditionally included CSS
       className  // and also add the classes passed in by props
    )

We add className last as a convention in this library because we always want the styles that come in through props to be applied on top of other styles. There are several examples of this throughout react-uswds codebase to check out too if you want.

[haworku]

Swap with usa-link__nav

[SirenaBorracha]

@suzubara do we use Happo differently with this project than on MM?

[brandonlenz]

This looks great!

One question to double check on the change to the tsconfig.json, otherwise I'm good to approve!

Congrats on your first react-uswds PR 💯