Preserve visually hidden text within license link

[thibaudcolas]

In the current editor output, the sanitize-html filtering causes the visuallyhidden class to be removed:

<a href="https://creativecommons.org/publicdomain/zero/1.0/legalcode" target="_blank">
  Creative Commons Zero v1.0 Universal <span>(opens in a new window or tab)</span>
</a>

I looked at what might be the correct fix based on the sanitize-html docs for allowedClass, but didn’t actually test this code.

There are two alternative fixes here that might be better suited:

• Remove sanitizeHtml altogether. At least currently this code only outputs content from spdx-license-list, which I’d assume is trusted enough with how they define URLs and license names.
• Remove the target="_blank" and <span>(opens in a new window or tab)</span> for simplicity.

[mgifford]

Interesting.. This looks good. I haven't tested it, but makes sense that it would be a problem in Svelte. Thanks @thibaudcolas