Add Horizontal Scrollbar to Memory Layout Viewer

[mrpopogod]

I tried out this feature that was added in #189 and it's really cool. However, I noticed that it doesn't have the ability to horizontally scroll, which becomes an issue when you have structs of structs of structs and the final primitives are many levels deep. This already comes up in the default "open as second pane" when looking at a struct with a String field; the final *const u8 is off screen. With a deeper nesting I could have components offscreen even with full window width.