Add `:local-link` pseudo selector

[Schweinepriester]

• Spec: https://drafts.csswg.org/selectors/#local-link-pseudo
• Chrome
  • https://chromestatus.com/feature/5194826811965440
  • https://groups.google.com/a/chromium.org/g/blink-dev/c/z2Y7O5ZCxgc/m/cj0paGiPAQAJ
• Firefox
  • https://groups.google.com/a/mozilla.org/g/dev-platform/c/mQNT-5RxHVM/m/7bYxZp50BAAJ
  • CSS Selectors 4: :local-link pseudo class mozilla/standards-positions#862
• Safari
  • CSS Selectors 4 :local-link pseudo WebKit/standards-positions#405

:local-link has been mentioned before in #1058, so technically this could be considered duplicate of that issue, but I'd argue for sub-issue now, given recent intent to prototype by two browsers 0:-)