[tui] scroll infra

[nazmulidris]

Implement scroll view or component. Currently each component is responsible for its own scrolling which isn't great. Also figure out how this works with OffscreenBuffer, if that can help radically simplify things.

Additionally, the issue of scroll view / pane / component needs to be addressed here as well. Currently scrolling is handled per component, which is awful, unergonomic, and error prone. It would be better if the scrolling logic could be abstracted elsewhere and the mental model of having a larger canvas, and a smaller viewport looking into it, might end up being so much easier to implement as well.

The terminal_async Readline enables word wrap and thus becomes a multiline editor. However, in a TUI context, this might be undesirable. So there's a challenge here to figure out how to implement scrolling using the mechanism (outlined above) that can be used by Readline as well.

This is a big topic that's needed attention for a long time.