Tables: focused headers scroll into view; long tables scroll sideways

A sortable header is a tracked Tab stop; once focused it sets its
table's sideways offset whole from its painted bounds and asks one
frame. The virtualized branch scrolls sideways too, and its list
keeps a plain wheel to its rows. layout::on_axis keeps a scroll box's
wheel to its axes; tables, code blocks, the thumbnail strip and the
gallery's page use it. Footer figures move to tables/foot.rs; the
profiler's ruler takes theme.chart().label. HumanInputRequest's
answered state gets a test.

src/layout/scroll.rs

@@ -16,6 +16,12 @@ use crate::{motion, theme::ActiveTheme};
 
 const IDLE: Duration = Duration::from_millis(900);
 
+/// Keeps a scroll box's wheel to its own axes; gpui turns a wheel along the other axis onto a box that scrolls one way, while the page scrolls too.
+pub fn on_axis<E: Styled>(mut element: E) -> E {
+    element.style().restrict_scroll_to_axis = Some(true);
+    element
+}
+
 struct Activity {
     handle: ScrollHandle,
     last: Point<Pixels>,