Updated hairline code to match latest cairo hairline patch:...

Updated hairline code to match latest cairo hairline patch: https://gitlab.freedesktop.org/cairo/cairo/-/merge_requests/21

cairo_set_hairline(true) has been replaced with cairo_set_hairline() and cairo_set_hairline(false) must be replaced with cairo_set_line_width. The changes in Inkscape here follow that same interface.