Shared geometry for stacking panel-corner “furniture” clear of each
other — annotation_scale()/annotation_attribution()’s scale bar and
attribution text, bivariate_legend()’s square guide, and an ordinary
legend placed with legend_position_inside — so two of them anchored
to the same or adjacent corners don’t draw on top of one another
(sipemu/ggplot-rs#273).
Text-metric helpers for axis-label fit (B3-1): ggplot-rs owns the
outer-label-overflow and check.overlap logic centrally, instead of a
downstream consumer post-processing rendered SVG (the old approach had
to re-parse <text> elements out of the markup).