doc: improve fragment (`:target`) anchors behavior on HTML version

This commit aims to improve the UX when navigating the docs using links to subsections. Previously the browser would scroll down to the section body, skipping the section heading. Using scroll-margin-top CSS property, we can fix this behavior (at least on some browsers).

Links to other versions are now updated with the current targeted hash to improve the UX when navigating from docs of one release line to another.

I've also removed syntax not parsable by older browsers (arrow functions and array destructuring) since the diff is pretty small and should improve UX on those browsers.