Add highlight markers in <?AuthorQuery?> positions - LEAN-992

This is to fix LEAN-992 (Inline AuthorQuery Comments positioned incorrectly).

The problem is that the selector has a value relative to a parent block, not the whole document.

This MR is to add a highlight marker in AuthorQuery position. So in the frontend (https://gitlab.com/mpapp-public/manuscripts-frontend/-/blob/master/src/hooks/use-comments.ts#L272) we can find that marker in the actual document and then put the icon in the right place.