Walks a renderable list (a flat list of renderables, a hemilist,
or a single renderable) and converts everything that is an
fs.coloredpaths instance to scimesh line layers. Non-line renderables are
ignored, they are handled by coloredmeshes_to_scimesh.
renderables_to_line_layers(renderables, style = "default")a list of scimesh line layers, possibly empty.
a renderable, or a (possibly nested) list of renderables.
a rendering style, see get.rglstyle.