Bug 1805392 - Fix outline-style: inherit behavior if you don't specify outline-width. r=Oriol

The fix is calling set_outline_style so that we also reset the actual
outline width. Also clean-up surrounding code a little bit to be
marginally more efficient, and do the same change for border-*-style
(which was doing the right thing, but it's better to make sure both stay
in sync).

Differential Revision: https://phabricator.services.mozilla.com/D164554