Lay n panels of aspect aspect (height / width) into an
area_w × area_h facet area, each panel topped by a strip_h strip and
separated by gap_x / gap_y. With ncol = None the column count is
the one that gives the largest panels (ties: fewer rows); a given ncol
is clamped to 1..=n. Every panel is panel_w × panel_h, with
panel_h = panel_w × aspect.
The natural height of a facet_wrap area of fixed-aspect panels at
width: the column count (a given ncol, else as many columns as keep
each panel at least min_panel_w wide, at most n) and
nrow × (panel_h + strip_h) + (nrow − 1) × gap_y for panels filling the
width. Lets a host size a faceted map before rendering it.