Blender Git Loki

Geometry Nodes: Initial implementation for attribute math node

This provide a simple implementation for basic math operations. Add,
subtract, multiple, and divide are implemented so far. Domain
interpolation is not implemented yet either.

This commit also adds two "Type" options to the node for choosing
explicitly whether to use an attribute or a float value as one of the
inputs. It is not possible to use two floats as inputs, because that
would be a regular math node.

Some cleanup to avoid some code duplication will come in a future
commit.