identity

Adds the identity property definition:

import {DefineMap, Reflect} from "can";

const Todo = DefineMap.extend("Todo",{
    id: {type: "number", identity: true},
    name: "string",
    complete: "boolean"
});

var todo = new Todo({id: 6, name: "mow lawn"});

Reflect.getIdentity(todo) //-> 6