Provide a 'hide all, show one' option for cloze deletions?

If such an option existed, it would allow users to more easily elide all but a single cloze at a time. Currently they are using nested clozes to approximate this, and it performs poorly+is limited in nesting depth.

One big question is how this might be implemented. If it were some flag in individual clozes, it would be confusing if a field had a mix of the two. We could potentially do it as a separate cloze notetype, though it would be a little awkward to switch between the two. Thoughts?

Originally reported on https://forums.ankiweb.net/t/nested-clozes-doesnt-work-for-more-than-3-nests/52661/11