Add H·T·M·L microdata to archive children

These attributes (`@itemscope` and `@itemtype`) are normally added at
the beginning of expansion to the root node of the document, prior to
it being wrapped. With archives, they should be added to archive
children as part of the processing which happens during application,
just prior to the wrapping which likewise occurs there. Having these
attributes present is important for title microdata processing (which
happens as a part of wrapping) to work correctly.

As part of this work, microdata handling is improved slightly in all
cases.

Note: If the `@itemscope` or `@itemtype` attributes were already
present on the children of the archive element, for example because
the child was the result of an embed, they will not necessicarily be
adjusted. It’s necessary to remove any embed typing during normal
processing if document typing is desired during the application phase.