Allow setting the PropertyInfo class_name from GDScript

modules/gdscript/gdscript.cpp

@@ -1453,6 +1453,9 @@ void GDScriptInstance::get_property_list(List<PropertyInfo> *p_properties) const
 					if (d.has("usage")) {
 						pinfo.usage = d["usage"];
 					}
+					if (d.has("class_name")) {
+						pinfo.class_name = d["class_name"];
+					}
 
 					props.push_back(pinfo);
 				}