a11y updates to full-text-search pages

[StephDriver]

closes #4839

[StephDriver]

A11y Syntax Notes

OLH theme has space around sections, so when they are put in to make landmarks, this can cause layout shifts. So now we have a class for when these are being used 'invisibly' to provide landmarks.

section.invisible-landmark{
  padding: 0;
  margin: 0;
}

Currently this is only a concern on OLH, as the other two themese don't ahve spacing, however it may be useful to extend this to all three themes and markup any sections that are purely to provide aria landmarks with this class.

[joemull]

Looks good. Found a few small bugs, and also added a few comments about readability around keeping this code distinct from the templates and patterns that belong to GenericFacetedListView, which granted are not very well documented as belonging specifically to it!

[mauromsl]

nice, just one comment regarding the value "all" for the pagination queryparameter

[mauromsl]

In terms of implementation, qs.count() is always preferred for querysets over len(qs)

I wonder, however, if we really want to support "all" as a feature, since we do not have a dynamic loader for this, we could put a lot of strain on the server. I don't think the user will be happy waiting for potentially thousands of results to be returned and displayed all at once

[StephDriver]

We use if paginate_by == "all" in several places, in commits spanning several developers over several years.

While you raise a good point, I think addressing it here is out-of-scope, and that should be its own issue, considered through triage etc, as to whether to change our practice and update across the whole codebase. Using it here is consistent with its use elsewhere.

[mauromsl]

fair enough, we still want articles.count() over len(articles) to avoid the implicit query and then we are good to merge

[mauromsl]

One last tidbit + one conflict resolution before we can merge