Fix Process List "Big" variant showing connected line

[aduth]

Merges to (blocked by) #356

Fixes an issue where Process List "Big" variant would show with the connected line when not rendered in prose content.

Issue can be seen here ("Big" should not show line): https://idp.dev.identitysandbox.gov/components/inspect/process_list/preview

Issue can't be seen here, since design system documentation is shown in .usa-prose: https://design.login.gov/components/process-list/#big

The underlying issue is a CSS specificity conflict, where the styles responsible for unsetting the border width were only strong enough to override the previous border width styling when rendered inside .usa-prose, but not when rendered outside .usa-prose. The changes here make it so that the "Big" border is only applied to the connected process list.

Testing Instructions:

1. Go to https://federalist-340d8801-aa16-4df5-ad22-b1e3e731098e.sites.pages.cloud.gov/preview/18f/identity-design-system/aduth-fix-process-list-big-connnected/process-list/#big
2. Observe the Big Process list shows without border
3. In DevTools console, enter document.querySelector('.usa-prose').classList.remove('usa-prose')
4. Observe the Big Process list still shows without border

[eric-gade]

@aduth I think the federalist link for testing the fix per the instructions expired

[eric-gade]

code changes look good to me

[aduth]

@aduth I think the federalist link for testing the fix per the instructions expired

Thanks for catching! It got outdated in some of the path shuffling with #358. I updated the link in the original comment.

[eric-gade]

Ok sweet, and the live test is working on my end. All looks good.

[zachmargolis]

LGTM