Geometry Nodes: Add names to String to Curves instance geometries

The name of each instance geometry is the character. This makes debugging
in the spreadsheet much easier, and the objects from "Visual Geometry to Objects"
are actually usable too.

Pull Request: #135599

source/blender/nodes/geometry/nodes/node_geo_string_to_curves.cc

@@ -294,6 +294,14 @@ static Map<int, int> create_curve_instances(GeoNodeExecParams &params,
     }
 
     GeometrySet geometry_set = GeometrySet::from_curves(curves_id);
+
+    {
+      const char32_t char_code[2] = {layout.char_codes[i], 0};
+      char inserted_utf8[8] = {0};
+      const size_t len = BLI_str_utf32_as_utf8(inserted_utf8, char_code, sizeof(inserted_utf8));
+      geometry_set.name = std::string(inserted_utf8, len);
+    }
+
     handles.add_new(layout.char_codes[i], instances.add_reference(std::move(geometry_set)));
   }
   return handles;