Bug - Tabs - move "box" borders from link to list item, fix HC styles

[mcoker]

Currently the "box" borders are on the tab link/button's ::before pseudo element, and those should be able to go to the parent list item instead.

Currently the high contrast border styles on the link/button are not using the correct tokens due to being directly on the link/button - if we freed up the ::before element, we could move the HC border styles to ::before and use the correct tokens.

[github-actions[bot]]

This issue has been automatically marked as stale because it has not had activity in the last 60 days.