shapes.rs: Use a session for logging where we have a DrawingCtx
shapes.rs: Use a session for logging where we have a DrawingCtx

Still to change is the implementation of Path::set_attributes() - but
we don't have a DrawingCtx at that stage.  Maybe we need to pass the
session to all the set_attributes() functions.

Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/731>

GNOME/librsvg,GNOME/librsvg,GNOME/librsvg,GNOME/librsvg