Bundle font registration, HTML dependencies, and
font family names into a single object. Each argument accepts
a font_google() specification, a font_liberation() specification,
or a plain character string naming a system font already available.
The returned object provides fields ready to use with
ggplot2::theme() ($sans, $serif, $mono),
girafe(fonts = ...) or dsvg(fonts = ...) ($dsvg_fonts),
and girafe(dependencies = ...) ($dependencies).