Add the ability to use next and previous buttons for SlideshowView.
Review Request #13165 — Created July 31, 2023 and submitted
The SlideshowView implementation ported over from rb-website assumed
that the nav was basically a table of contents, with a nav item for each
slide. This change adds functionality to use next/previous buttons
instead (you cannot currently use both).
Used in conjunction with a change that adds a slideshow to the review
dialog.