Blender Git Loki

Geometry Nodes: remove accidental exponential time algorithm

Calling `foreach_field_input` on a highly nested field (we do that
often) has an exponential running time in the number of nodes.
That is because the same node may be visited many times.
This made Blender freeze on some setups that should work just fine.
Now every field keeps track of its inputs all the time. That replaces
the exponential algorithm with constant time access.