Geometry Nodes: Add string input node

This commit adds a simple string input node, intended for use in the
attribute workflow to make using the same attribute name in multiple
places easier. The node is function node similar to the existing vector
input node.

Ref T84971

Differential Revision: https://developer.blender.org/D10316

release/scripts/startup/nodeitems_builtins.py

@@ -508,6 +508,7 @@ geometry_node_categories = [
         NodeItem("GeometryNodeCollectionInfo"),
         NodeItem("FunctionNodeRandomFloat"),
         NodeItem("ShaderNodeValue"),
+        NodeItem("FunctionNodeInputString"),
         NodeItem("FunctionNodeInputVector"),
         NodeItem("GeometryNodeIsViewport"),
     ]),