Nodes: rename structure type to shape in node group inputs ui

This was discussed in the recent Geometry Nodes workshop. The term "shape"
is only used here because it literally affects how the socket will look like.

source/blender/editors/space_node/drawnode.cc

@@ -1471,7 +1471,7 @@ static void std_node_socket_interface_draw(ID *id,
     sub->active_set(!is_layer_selection_field(*interface_socket));
     sub->prop(&ptr, "hide_in_modifier", DEFAULT_FLAGS, std::nullopt, ICON_NONE);
     if (nodes::socket_type_supports_fields(type) || nodes::socket_type_supports_grids(type)) {
-      sub->prop(&ptr, "structure_type", DEFAULT_FLAGS, std::nullopt, ICON_NONE);
+      sub->prop(&ptr, "structure_type", DEFAULT_FLAGS, "Shape", ICON_NONE);
     }
   }
 }