Improve handling of scroll points across pages

[typesanitizer]

Enhancement

Short description (2-3 lines)

Scrolling points should be saved on a per page basis. When you enter a page for the first time, you should start at the top, not in the middle. Right now, it looks like they're saved on a global basis somehow (is it a viewport property?).

Suggested test cases, if any

Try using stack -- its help page is quite long and consulting the subcommand help pages is an unnecessarily jarring experience.