add a GVLayout class with construction from AGraph and GVContext objects
The GVLayout class is an RAII-class that performs a layout using
shared pointers to AGraph and GVContext objects. It participates in
the handling of the lifetime of those objects, since it needs them to
free the layout when the GVLayout object is destroyed. It currently
supports construction with built-in plugins, move construction and
move assignment, but not copy construction or copy assignment since
the AGraph and GVContext objects do not support that.
Towards https://gitlab.com/graphviz/graphviz/-/issues/2001.
projects / graphviz / commit