Blender Git Loki

Geometry Nodes: add socket value logging capability

The node tree evaluator now calls a callback for every used socket with
its corresponding value(s). Right now the callback does nothing.
However, we can use it to collect attribute name hints, socket values
for debugging or data that will be displayed in the spreadsheet.

The main difficulty here was to also call the callback for sockets in
nodes that are not directly executed (such as group nodes, muted
nodes and reroutes).

No functional changes are expected.