Implement the equivalent of abline (plot line using slope/intercept only) to add line to graph

Currently there seems to be no way to add a line to an existing graph (e.g. as a new trace) based on slope and intercept and without the necessity to find out the actual ranges of x and y axes of the figure.
All examples I have seen so far are based on using existing x values of dots in a scatter plot, calculating the corresponding y values for the line and adding those line segments in a new scatter plot trace.

But this has two huge disadvantages:

• the y values have to get calculated for those x values (which may be a lot) or x values need to get selected
• if a lot of segmets are calculated, the graph complexity increases a lot as well

But plotting a line based on just slope and intercept is probably the second most easy thing to do, so there should be a way to add a line that way.

The basic signature of the corresponding method or class could be similar to the corresponding R function:
ABline(a=intercept, b=slope, h=yforhorizontallines, v=xforverticallines)

En el issue no se mencionan archivos ni tests. Empieza revisando la API de plotting existente y los tests para añadir líneas o trazas; después, compara su comportamiento con la firma de estilo R solicitada. Se considera terminado cuando se puede añadir una línea únicamente a partir de la pendiente/intersección, con opciones para líneas horizontales y verticales, sin requerir valores x muestreados ni una búsqueda manual del rango de los ejes.