Blender Git Loki

Geometry Nodes: Use highest complexity attribute in join node

This just implements a todo with a utility function that didn't exist
at the time. For example, if one geometry has a "scale" attribute with
a float type and another has a "scale" attribute with a vector type,
the vector type will be used for the resulting geometry.

Differential Revision: https://developer.blender.org/D10206