adding :scope to dom pseudoclass

For now in querySelector only a subset of css selectors are implemented, the :scope pseudo selector target the current element.

Use cases

const sections = event.document.querySelectorAll("section");
for (const section of sections) {
  const heading = document.querySelector(`
    :scope > h1, :scope > h2, :scope > h3,
    :scope > h4, :scope > h5, :scope > h6
  `);
  if(!heading) this.report("section need heading")
}