Blender Git Loki

Compositor: Graphviz improvements

Graphs are usually large, needing a lot of horizontal scrolling and
they can include more information for debugging.

This patch makes graph more compact horizontally by splitting
labels in lines and removing namespaces.
Furthermore it adds following information:
- Operation ID.
- SetValueOperation float value.
- Optionally, operation node name.

Reviewed By: jbakker

Differential Revision: https://developer.blender.org/D11720