Resolve a configuration object the plot code keeps in the global environment
Source:R/plots_utils.R
style_config_object.Rdconf/methods_plots_config.R and the run's methods configuration
assign with <<-, so the plot code reads them as free variables the way it
already reads font, dpi and textwidth. Returning NULL rather than
erroring lets the style helpers be called with an explicit table in tests,
where no configuration has been loaded.