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/chat/code.rs

@@ -10,6 +10,7 @@ use crate::{
     buttons::{Button, ButtonVariant, CopyButton, IconButton},
     editor::code_colors,
     forms::Run,
+    layout::on_axis,
     primitives::{Disclosure, IconName},
     theme::{ActiveTheme, ControlSize, Radius, TextSize},
 };
@@ -128,8 +129,7 @@ impl RenderOnce for CodeBlock {
                     .child(CopyButton::new((self.id.clone(), "copy"), code.clone())),
             )
             .child(
-                div()
-                    .id((self.id.clone(), "code"))
+                on_axis(div().id((self.id.clone(), "code")))
                     .overflow_x_scroll()
                     .px_3()
                     .py_2()