This helps to keep the prelude small and less likely to conflict with
other crates.
- remove widgets module from prelude as the entire module can be just as
easily imported with `use ratatui::widgets::*;`
- move prelude module into its own file
- update examples to import widgets module instead of just prelude
- added several modules to prelude to make it possible to qualify
imports that collide with other types that have similar names
Represents a scrollbar widget that renders a track, thumb and arrows
either horizontally or vertically. State is kept in ScrollbarState, and
passed as a parameter to the render function.
