The sticky header/footer wrapper width was narrowed by a separately
JS-measured scrollbar size, while the column widths shared via colgroup
were computed against the browser's own `scrollbar-gutter: stable`
reservation used by the body div. These two numbers aren't guaranteed to
agree, and when the probe overstates the real reservation the fixed-layout
table overflows its `overflow: hidden` wrapper, clipping the rightmost
column -- typically the totals row once a chart is resized enough to need
a vertical scrollbar.
Header and footer now reserve space via the same `scrollbar-gutter`
property the body already uses, so all three always agree.
Fixes#21063
sadpandajoe