The timeline's scroll box is the flex row itself, so its reach is its
shots; a focused shot brings itself whole into view through
layout::bring_into_view, which table headers now share; Extend sits
with the caption under the strip. A voice's tags cap at the row's
width and wrap inside it.
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.
ZacharyZhang-NY