6c00e0fda4
This is a major departure to how page previews used to work. Add a new layout manager that handles showing and hiding page previews and navigation arrows. Move most of the code handling page previews to this new layout manager. The layout manager allocates at most 20% of the screen width for the previews, and at least the width of the arrow. The next and previous page peeking effect is temporarily lost with this commit, but will be reintroduced in later commits. Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2335>