Incorporates my contribution that removes the word boundary requirement
after the prefix and before the suffix; see PR #148:
<https://github.com/WICG/scroll-to-text-fragment/pull/148>

Chromium’s implementation currently does not trigger when clicking links
pointing to quotes within the same page. As a workaround, listen to link
clicks, and activate the polyfill when a link points to a fragment within
the same page.

As the polyfill uses the window’s selection to highlight the target(s),
this only works in Firefox, as other browsers do not support selections
having multiple ranges.

Moves window.location.fragmentDirective to document.fragmentDirective

Based on the Text Fragments draft spec version of 12 Aug 2020.