A rendered axis control group: which axis, its ordered options, and the
value Reset restores (the axis' own library default). This is a
discriminated union on axis, so options and reset are typed to that
axis' value union - a { axis: 'density', reset: 'x' } is a compile error,
not a garbage value written to <html data-density>. Reorder or drop axes
by supplying a subset via withA11yPanelAxes.