ui: More component previews, UI component cleanup (#25302)

- Don't require ui component docs (this isn't really working)
- Add more component previews
- Update component preview style & navigation

Release Notes:

- N/A

crates/ui/src/components/scrollbar.rs

@@ -1,4 +1,3 @@
-#![allow(missing_docs)]
 use std::{any::Any, cell::Cell, fmt::Debug, ops::Range, rc::Rc, sync::Arc};
 
 use crate::{prelude::*, px, relative, IntoElement};